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OBSERVATIONS ON STRUCTURE OF CELLS AND NUCLEI. 3 1 5

152. Semper.—Ueber die Entstehung der geschichteten Cellulose-Epi-dermis der Ascidien, Semper's ' Arbeiten,' B. ii, p. i. 1875.

153. Id.—Die Verwandtsehaftsbeziehungeu der gegliederten Tkiere,Ibid, B. Hi. 1876.

154. Slrasburger.—Ueber Zellbildung und Zelltheilung. Jena, 1876.155. Id.—Ueber Befrucktimg und Zelltheilung,, ' Jenaische Zeitschr.,'

B. xi, p. 435. 1877.156. Villot.—L'histologie de l'oeuf, ' La Kevue des Sci. Nat.,'Tome v,

Dec, 1876.157- Weisxnunn.—Die Entwicklung der Dipteren im Eie, nach Beobach-

tungen an Chironomus, ' Zeitsehr. f. wiss. Zool.,' B. xiii. 1863.158. Zeller.—Untersuchungen iiber die Fortpflanzung der Opalinen,

' Zeitscbr. f. wiss. Zool.,' B. xxix, p. 352. 1877.159. Id.—Weiterer Beitrag zur KemitnissderPolystomen,t&!cf, B. xxvii,

p. 238. 1876.160. Dim.—Die Entwicklung des mittleren Keimblattes im Hiihnerei,

' Arch. f. Mile. Anat.,' B. xv. p. 67. 1878.161. Van Beneden.—A Contribution to the History of the Embryonic

Developmeut of the Teleosteans, ' Quart. Journ. Mic. Sci.,' vol. xviii, N.S., Jan., 1878.

162. Ratzel and Warcheasky.—Zur Entwicklungsgesohichte des Regen-wurms, ' Zeitschr. f. wiss. Zool.,' B. xviii, p. 547. 1868.

OBSERVATIONS on the STRUCTURE of CELLS and NUCLEI.By E. KLEIN, M.D., F.R.S. (With Plate XVI.)

I.THE knowledge of the structure of cells and cell-nuclei

has of late years been greatly extended hy the observationsof Kleinenberg, Eimer, Heitzmann, Auerbachj Strassburger,Frommann, Schwalbe, Butschli, O. Hertwig, R. Hertwig,KupfFer, van Beneden, W. Flemming, Eberth and others. Itis shown by the work of these observers that the substanceof cells, as well as that of their nuelei, is of a far morecomplex nature than is indicated by the term ' granular' or' hyaline'—usually applied to it.

Heitzmann1 asserts that the substance of various cells—amoebae, blood-corpuscles, cartilage cells, bone cells, epithe-lial cells, &c.—contain networks of minute fibrils, into whichpass fibrils radiating from the interior of the nuclei of thosecells. Kleinenberg, W. Flemming, O. Hertwig, and E. vanBeneden/ observed a network of fibrils in the nucleus of theovum of various invertebrate and vertebrate animals.

1 " Untersuehungen iiber das Protoplasma," ' Sitzungsber. d. k, Akad. d.Wiss. Vienna,' Bd. lxvii and Ixviii, Abt.h. iii, 1873.

2 ]?or the detailed references sec W. Flemming's paper in 'Archiv f,Mikrosk, Anatom.f' Bd. xiii, p. 715..























































3J6 DR. E. KLEIN.

Fronimann1 describes, in accordance with Heitzmann, aminute network of fibrils in the nuclei of blood-corpuscles ofAstacus Jltiviatilis ; this network passes through the nuclearmembrane into a similar network of the substance of theblood-corpuscles. From a reference quoted in a note (" ZurKenntniss des Zellkerns"), by Professor W. Flemming, in• Centralblatt f. med. Wissen.,"' 1877, No. 20, I learn thatC. Frommann had observed and described already in 1867,i.e. before Heitzmann, a network of fibrils in the nuclei ofmany kinds of cells.

Butschli2 observed in the neuclei of coloured blood-corpus-cles of frog and newt minute fibrils with granular thicken-ings, but no nucleolus, as asserted by Ranvier.

Schwalbe1 made extensive studies on the nuclei of gan-glion-cells of the retina and found their nucleoli often pos-sessed of minute filamentous prolongations; the nuclearmembrane shows prominences on its inner surface. Nucleolusand filaments, nuclear membrane and its prominences repre-sent what Schwalbe designates as ' Nucleolarsubstanz,' andhe distinguishes it from the rest of the nuclear matter,which he calls 'Kernsaft' (nuclear juice). Schwalbe thinksthat this arrangement of the 'Nucleolarsubstanz' is broughtabout by a process of vacuolation, which in young indivi-duals is of much greater extent than in older ones. Accord-ing to Schwalbe between the bulky mass of the nucleoJarsubstance in small young nuclei and the small rudiments •of this same substance—limited entirely to the membrane ofthe adult nuclei, in which the nucleolus is not presentany more, there are intermediate stages brought about hyvncuolation, one of which is the above-mentioned condition,viz. nucleolus with processes, smaller or larger prominencesop the inner surface of the nuclear membrane.

Kupffer4 maintains of the liver cells of frog, of the odon-tohlasts, of the epithelial cells of the urinary tubules, and ofthe cells of salivary gland of Periplaneia orientalis, thattheir substance is composed of a hyaline (non-fluid) groundsubstance, 'Paraplasma,' and of a granular-fibrillar contrac-tile ' Protoplasma' embedded in the former. The relation

1 "Zur Lehre von der Structur der Zellen," 'Jeuaiscke Zeitsclirift f.Naturw.,' Bd. ix, p. 2S0.

- " Studien iiber die ersten Eritw," &c, ' Abhandl. d. SenkenbergisclienNaturf. Gesellsch.,' Bd. x.

3 "Bern, iiber d. Kerne d. Ganglienzellen," 'Jenaische Zeitsclirift f.Naturvf,.' Bd. x, p. 25.

* " VSbet Differeuzirung d. Protoplasma an den Zellen thierischer Gew."' Scliriften des Naturw. vcreins f. Schleswig-Holstein.,' Heft iii, und.•Beitr. z. Anaf. u. Physiol. Festsiir. f. Carl Ludwig/ 1875.


and distribution of the protoplasmic fibrillar substance varieiin the cells of different kinds.

R. Hertwig1 and Biitschli3 distinguish, like Schwalbe,the former a ' nuclear substance' from a ' nuclear juice,' thelatter a 'nuclear matter' from a 'nuclear fluid.' The 'nuclearmatter' of Biitschli comprises the nuclear membrane, thenucleolus and a fibrillar stroma; the latter in some instancesextends and a radial manner from the nucleolus.

E. van Benedens saw a fine protoplasmic reticulum in thelarge axial entodetm cell of Dicyema, which (reticulum)exhibited slow spontaneous movements. In the nucleus ofthe ripe ovum of Asterocanthion rubens, v. Benedenobserved within the nuclear membrane and besides thenucleolus a delicate network of a finely granular substance,' Nucleoplasma,3 including several ' Pseudo-nucleoli.' Alsothe germinal vesicle of the ripe ovum of rabbit contains aminute network.

Arndt ('Uber den Zellkern. Sitzung. d. medicin. Vereinszu Greifswald,' Nov., 1876), distinguishes in the nucleus ahomogeneous ground substance and elementary globules;the former possesses a reticular structure and encloses in itsmeshes the latter.

W. Flemming* made very important observations on thestructure of the nuclei found in the membrane of theurinary bladder of Salamandra maculata. This author, towhose paper I shall have to refer more minutely hereafter,saw a very delicate and dense network of fibres uniformlypervading the interior of the nucleus and attached to the nu-clear membrane. This uetwork—' Geriistformige Structur'—was seen by Flemming in the nucleus of all cellular elementsof the bladder of Salamandra—epithelial cells, connective-tissue cells, migratory cells, unstriped muscle-cells, nerve-cells, endothelial cells and blood-corpuscles.

The clearness and extent of the observations of this authorleave no doubt that the network in the nucleus represents adefinite and pre-existing structure. Although this is to acertain extent questioned by Langhans6 as regards the freshcells of the human decidua serotina, Flemming's assertionscannot be, I think, in the least shaken, considering that heobserved the above structure, not only after the use of

1 'Morpholog, Jahrbucher,' vol. ii.5 L. c, vol. x.3 ' Bulletins de I'Acadfimie roy. de Belg.,' 2 s6r., t. 41, No. 1 and No. 6,

1876.4 " Beobacktungen iiber die Bescbaffenheit des Zellkernes," 'Arcbivf.Mikrosk. Anatomie,' Bd. xiii, p. 693 and following.

s Langhans, 'Centralbl. f. Medic. Wisseusch./ 1876, N. 50.

318 DR. E. KLEIN.

reagents, e.g. acetic acid, chromate of potash, alcohol,chromic, acid with or without subsequent staining in carmineor haematoxylin, but in the absolutely uninjured bladder, i.e.,while this organ was being observed in the living (curarised)animal. In a subsequent note ("Zur Kenntnis des Zellkerns")in ' Centralblatt f. medic. Wiss.,' 1877, No. 20, Flemmingstates that he observed the same network in the nuclei ofvarious cells also in the living and perfectly uninjured larvaof Salamandra.

In StrassburgerV great work (' Uber Zellbildung undZelltheilung,' Jena 1875), we notice in developing cells ofPhaseolus multifiorus a network of fibrils radiating fromthe nucleolus, permeating the interior of the nucleus in con-nection with a similar network of the cell-substauce.

Mayzel2 met in the epithelium of the cornea of frog, rabbitand cat, during regeneration, with large round nuclei, inwhich he observed filamentous masses either in a convolutedmanner or radiating from a central point. Mayzel regardedthese forms as due to a particular stage of division, as de-scribed by Biitschli and Strassburger.

Eberth3 noticed similar nuclei in the epithelium of theuornea and the endothelium of the membrana Descemetiunder normal and abnormal conditions, i.e. nuclei containinganastomosing filaments in their interior. Eberth also regardsthem as peculiar forms in the development and division ofnuclei.

Eimer* found in numerous nuclei that the granules of the' granular zone' surrounding his 'hyaloid' are due to proto-plasmic filaments, which permeate the interior of the nucleusand anastomose with each other so as to form a network.This network extends to the membrane of the nucleus, andalso sends radiating fibrils through the hyaloid into thenucleolus. Such or similar is the condition in the nucleusof ciliated epithelial cells of the palate of Salamandramaculata, in those of cells lining the inner surface of thetentacular wall of Aegineta, the sensory cells and the ecto-derm-cells of Carmarina hastata and others. The networkof fibrils of the nucleus is in some instances also in connectionwith fibrils and networks of such, belonging to the cell-sub-stance itself.

1 For an excellent abstract-see Mr. J.Priestley in this Journal, Vol. XVI,p. 133, aud Plate XII, figs. 1—6.

•- ' Centralbl. f. Medic. Wiss.,' N. 50,1875.3 "Uber Kern- und Zelltlicilunjr," ' Virchow's Archiv,' Bd. 67.4 "Weitere Nachricliteu uber den Bau des Zelkernes," &c, 'Archiv f.

Mikrosk. Anatomie,' Bd. xiv, p. 94. See also " Notes and Memoranda " qfApril Number of this Journal, 1878.

OBSERVATIONS ON STltUCTUHE OF CELLS AND NUCLEI. 3 1 9

In the present paper I propose to show by a simple methodand on an object easily attainable at all seasons of the yearthat the statements of Professor Fletnming, of Kiel, abovequoted, as regards the delicate network of fibrils more or lessuniformly pervading (he interior of the nucleus of variouscells is in all respects perfectly correct. In addition to thisI shall have to notice several observations I made withreference to the structure of the cell-substauce itself and therelation of it to the intranuclear network.

A The stomach of a freshly killed newt {Triton crislatus)is cut open and placed into a 5 per cent, solution of chromateof ammonia in a closed vessel—(a reagent now well knownthrough the investigations of Heidenhain1 on the rod-likestructures in the epithelium of some of the urinary tubules,and afterwards used by MacCarthy2 for the demonstration ofthe rods in the medullary sheath of nerve-fibrils)—where it iskept for about, twenty-four hours. It is then washed inwater for about half an hour and placed after this in a dilutesolution of picro-carmine, where it is left till it assumes adeep pinkish-yellow tint. It is now washed in water, andmicroscopic specimens are prepared in this manner:—Themucous surface of the organ is scraped with a small scalpel,whereby smaller or larger flakes may be easily removed; theyare placed in a very tiny droplet of glycerine on a glass slide jby slight knocking with the rounded or flat top of any thinrod or needle holder these flakes are broken up into micro-scopic fragments ; a drop of glycerine is placed on a covering-glass, and this is inverted over the above specimen.

Examined under a moderately high power—say Hartnack's7 or 8, or Zeiss's D or E—we recognise easily innumerableisolated or groups of epithelial cells, and a great manyisolated nuclei or fragments of nuclei. If the scalpel hasbeen drawn over the surface of the mucous membrane witha little energy, the preparation contains great numbers ofgland-cells, isolated and in continuous masses, and also otherelements belonging to the tissue of the mucosa.

1. What arrests the attention of the observer at once is thestriking appearance presented by all nuclei, every one of themshowing an extremely beautiful network of fibrils, which per-meates its interior uniformly. In some instances this network,which we will designate ' intranuclear network] does notextend quite up to the nuclear membrane, which in allinstances is well defined, but leaves a narrower or broader

1 ' Archiv f. Mikrosk. Anatom./ Bd. x, 1S73,' This Journal, 1875, p, 377.

3 3 0 DR. E. KLEIN.

zone next this membrane unoccupied. But in all cases thenetwork is in connection with what is known as the limitingmembrane by numerous fibrils. These connecting fibrilsappear naturally longer in those instances where the intra-nuclear network does not reach up to the nuclear membrane.The network stains a pink colour; the colour is more pro-nounced, caeteris paribus, the more shrunk the network is,but apart from this some portions of the network are staineddeeper than others.

The fibrils of this network are highly refractive, and varyin their thickness, course and arrangement. In some nucleithey are delicate, fine, cylindrical and smooth, or stiff andshort, and so densely arranged as to leave more or less uniformsmall spaces between them; in others they are coarse, mem-branous, and possessed of an irregular outline, are more orless convoluted, and so arranged that the spaces formed bytheir anastomoses are not uniform, being sometimes largerin the central parts of the network than in the periphery, atother times the reverse is the case. There are nuclei in whichthe fibres appear to possess a spiral or circular arrangementin the periphery of the network. Seen from the narrowerside, some nuclei—especially those of the surface-epithe-lium—show a chiefly longitudinal arrangement of the fibresof the network. We find all forms between a network offibrils as represented, e.g. in a net, and a honeycomb of mem-branous structures, as represented in a sponge. In almost allinstances however, we observe a greater or smaller numberof minute bright spots, which as careful focussing provesare fibrils of the network seen in optical transverse sectionor at the point of anastomosis. But it seems also that somefibrils are possessed of irregular thickenings. This is shownwith remarkable clearness iu those instances in which thenuclear membrane has been broken at one or the other pointand the fibrils of the intranuclear network protrude throughthis opening. In fig. 8, of Plate XVI, such protrudingfibrils are shown. Comparing the different nuclei one cannothelp noticing that the number of the above-named brightdots is greater, the denser the network, the more convolutedits fibrils are, or the more shrunk the network is as a whole.

Numerous fragments of nuclei are met with in our pre-parations ; these consist of greater or smaller portions of theintranuclear network isolated from the nuclear membrane ;in fig. 3, Plate XVI (a, b, c), may be seen such isolated net-works.

The nuclei of the epithelial cells are slightly flattened, andwhen, therefore, seen in profile, they do not show the net-

OBSERTATIONS ON STRUCTURE OF CELLS AND NUCLEI. 8 2 1

work so clearly as when seen from thp surface. The net-work appears more delicate in the nuclei of the gland-cellsand endothelial plates of the mucosa than in those of theepithelial cells of the surface.

In some nuclei the ground substance, in which is embeddedtheintranuclear network, appears slightly tinged red, in othersit is perfectly colourless.

Such are the appearances presented by the nuclei of thesurface-epithelium, of the gland-cells, and of the endothelialplates of the mucosa of the stomach, prepared simply in 5 percent, solution of chromate of ammonia. Of the greatestclearness and distinction, and of greater preference as regardspreservation in microscopic specimens that are permanentlyto be sealed up, are the nuclei of the above cellular elements,if, after having been kept for about twenty-four hours in 5 percent, solution of chromate of ammonia, the stomach is placedfor abont J—l'hour in a mixture of 2 parts of l-6th percent, solution of chromic acid and 1 part of methylatedalcohol—a mixture which I am in the habit of using withgreat advantage for hardening glandular organs, and such ascontain connective- and muscular tissues—then washed andtreated as above.

But also by keeping the fresh stomach for twenty-fourhours in M tiller's fluid, washing and then staining it in picro-carmine, the intranuclear network may be perceived in somenuclei, although with far less distinctness than after theabove methods. In many nuclei the network is too muchshrunk and presents, therefore, the well-known 'granular'appearance. The appearance is somewhat, though not verymuch, improved by placing the stomach, after Miiller's fluidand before washing it, in the above mixture of chromic acidand spirit for about |—1 hour.

The nuclei examined in the perfectly fresh conditionshow distinctly, although faintly, part of the intra-nuclear network, a good magnifying power, as Zeiss's F orHartnack's Imm. 10, and good light, as that reflected by whiteclouds, being indispensable. Other reagents, as osmic acid,alcohol, chromic acid, bichromate of potash, give not verysatisfactory results, although osmic acid and bichromate ofpotash show the intranuclear network in some instances moreor less distinctly.

Measurements which I made of the nuclei in specimensprepared after the 5 per cent, chromate of ammonia methodand mounted in glycerine, give the following numbers as themean:

322 DR. E. KLEIN.

(a.) For the nuclei of surface epithelial cells 0'017 by0007 millimetres.

(5.) Nuclei of gland-cells 0017 by 0-014 mm.(c.) And the same numbers for those of endothelial plates.

There are several questions which suggest themselves inconnection with the observations just detailed: First, asregards the e granules' or bright dots that present them-selves in the intranuclear network, we have to ask whattheir exact nature is ? As has been mentioned alreadypreviously, many of the bright dots or granules can bedistinctly recognised as due to optical transverse sections offibrils, these being either twisted or bent, or being altogetherplaced vertically; this is the view also expressed by Flem-ming (1. c , p. 698). But I have no doubt that in somenuclei the more irregularly shaped dots are due to a thicken-ing of fibrils from place to place, the fibrils not being alwayscylindrical, but some showing a perfectly irregular outline.• It is clear from this that the more shrunk the intranuclearnetwork or the more twisted and convoluted the fibrils themore does the nucleus present the appearance of being'granular.' And it is, no doubt, owing to this conditionthat in hardened specimens we are able to distinguish some-times only a granular condition of the nucleus. Thus, forinstance, the ' granular' nuclei of epithelial cells, lymph-cells, unstriped muscle-cells, muscle-corpuscles, &c, ofdifferent organs in many animals, including man and mam-mals, are due merely to a shrunken or convoluted conditionof the intranuclear network, or to the fibrils having adense arrangement, as I shall have occasion to show on afuture occasion.

The few ' granules' that one also observes occasionallyin nuclei in a fresh condition are due to some of the fibrilsbeing seen in optical transverse section, the fibrils them-selves being not easily differentiable. A careful examina-tion with a good lens and a good light shows the correctnessof this in most cases. Thus, for instance, the examinationof the nuclei of fresh epithelium of frog, toad, or newt,the nuclei of fresh coloured blood-corpuscles of these animals,especially of toad, with a Zeiss's F Lens or a Hartnack'sImmersion No. 10, reveals fibrils in the nucleus, and alsoshows that the ' granules' are due to the twisted or bentcondition of them.

Another point which deserves consideration is the so-callednucleolus. It is well known that many nuclei of the mostdifferent kinds of cells contain a very conspicuous, highly re-


fractive, large dot, called nucleolus; the best known examplesare the nucleus of ganlion-cells and the germinal vesicleor nucleus of ovum. Many nuclei contain more than onenucleolus, which are described as of the same, or as is morecommonly the case, of different sizes. Now, to every ex-perienced student of histology it must have become apparentthat if there is one thing unsatisfactory, unreliable, puzzlingand inconstant about the nucleus of vast numbers of cells,it is this very nucleolus. Flemming (1. c , p. 702) maintainsthat in the case of the nuclei of the bladder of Salamandra'nucleoli' are present and may be demonstrated byanilin staining. But looking at his drawings (figs. 9, a, b,c, and d) I fail to see the justice of this conclusion. Whatis here shown in the nucleus are numbers (a dozen andmore) of more deeply stained, irregularly-shaped massesplaced in the fibrils of the network.

Thus, for instance, in d of his fig. 9, Flemming shows ustwo nuclei of unstriped muscle fibres, each of which containsin the network of fibrils, only faintly seen, an uncountablenumber of irregularly shaped particles. Why he shouldregard all these particles as definite anatomical structuresidentical Avith the spherical bright large spot, which isgenerally characterised as nucleolus, I fail to comprehend.Arguing against Schwalbe, Flemming (I.e. p. 713) thinks that" the nucleoli at all events do not represent merely localaccumulations of the network, but are or may be in manycases something different."

In the nuclei of the cells of the stomach of newt, preparedin the above manner, I do not find in the great majority ofinstances any signs of what is usually accepted as a nucleolus ;only in a few instances I saw one or two particles (larger thanthe ordinary bright dots above explained) which correspondto Flemming's ' nucleoli.' Now, I have after a very pro-longed examination arrived at the conclusion that theselarge particles are due to one of two things ; in some instancesthey are distinctly thickenings of the network, in othersthey appear to bo merely due to the shrivelling up and inti-mate fusion of a part of the network. And this seems tome to be borne out also by the examination of nuclei ofthe stomach or palate of newt in the fresh condition. Ihave seen distinctly that when the neucleoli are present—theinstances are fewer than is generally supposed—they are accu-mulations of the fibrils of the network. The inconstancy asregards size, shape and number of the so-called nucleoliseems to me to point very strongly in the above direction,viz. that they are due merely to a local thickening (natural

324 DR. E. &LEIM.

or artificial) of the fibres of the intranuclear network. Theobservations of Van Beneden, O. Hertwig, Schwalbe,Langhans, Flemming himself, and last, not least, Auerbachand Eimer, appear to me to lend support to the view thatin most cells the so-called nucleoli are local accumulations ofthe intranuclear network, that they are inconstant in size aminumber, and that they are only transitory appearances. Asregards this last point, the observations of Strassburger,Schwalbe and Langhans, may be here referred to, especiallyLanghans (1. a ) , according to whom the single nucleolus ormultiple nucleoli met with in the nuclei of cells of thehuman decidua serotina, are the result of the shrinking ofthe network.

The assertions that have been made as regards sponta-enous movements of nucleoli (Auerbach,1 Brandt,3 Ehner,3

Kidd,* and others) are quite compatible with the aboveview, for E. van Beneden, as previously mentioned, hasobserved movements in the intranuclear network, and it isquite possible that the above assertions might refer to con-tractions of part of the network.

A last point to be considered is the nuclear membrane init relation to the intranuclear network. I shall have tomention this more fully hereafter in connection with thecell-substance itself, but will limit myself here only to saythat the examination of the nuclei in my specimens,especially of nuclei that are isolated, and whose limitingmembrane has become broken at one place or another (seefig. 8, PI. XVI), shows that what usually appears as nuclearmembi'ane is composed of an outer thicker portion, whichis the limiting membrane proper, and—closely connected withit—of an inner, more or less incomplete—probably becausereticular—delicate layer, which is, properly speaking, a peri-pheral condensation of the intranuclear network, with whichit is, of course, connected by longer or shorter threads.The clear space which may be observed in some instancesbetween the ' membrane ' of the nucleus and the intra-nuclear network is due, as mentioned on a former page, to aretraction of the latter from the former, and is a space, notbetween the two layers of the limiting membrane, butbetween the inner layer of this and the bulk of the intra-nuclear network.

2. The following forms of cells present themselves in our1 ' Organologische Studien,' &c, Abth. 3, Breslau, 1874.a ' Arcbiv. f. Mikr. Anatom.,' Bd. x.» ' Archiv. f. Mikr. Anal.,' Bd. xi.4 This Journal, 1875.

OBSERVATIONS ON STRUCTURE OF CEL1S AND NUCLEI. 3 2 5

specimens :—a. Columnar epithelial cells varying somewhatin length and thickness ; they are goblet-cells of the same or asimilar character as those represented in figs. 1 and 2. Theyconsist of an upper swollen transparent part, and a lowerpart more opaque and including the nucleus. The first haslost its cover, the second terminates in a more or less inden-tated, serrated, or truncated manner. In some cells thenucleus lies close to the boundary line of the two parts, inothers there is a longer or shorter mass of protoplasm inter-posed between the two. In the latter case the cell has amuch more graceful form, being relatively less plump inboth parts. If the preparation be made by scraping theforegut, we meet also with a few ciliated cells, conical orcylindrical in shape. Most of the ciliated epithelial cells ofthe foregut, however, present themselves likewise as goblet-cells, the cover with the cilia having been removed.1

The columnar goblet-cells mentioned before may begrouped, according to size, in two distinct categories—onecomprising the larger, the other the smaller forms. Thelarger cells belong to the surface, the smaller ones to theducts of the gland. (Besides cells, which, to all appearancesare perfect, there are a good many, which present them-selves only as larger or smaller fragments.)

b. Flat transparent cells with nuclei somewhat larger thanthe nuclei of those mentioned above. These cells are metwith in groups forming the wall of larger or smaller portionsof gland-tubes; when in a group they are imbricated, andbeing flattened they do not appear conspicuous when thusseen in profile; their bulky nucleus seems to be the chief thingthat attracts attention. It is the nuclei of these cells whichshow the intranuclear network most splendidly. When thesecells are met with isolated and looked at in profile they are seento be composed of a bulky oval nucleus, to one pole of which isattached a short plump process, to the opposite pole one thatis many times longer. Some of these cells are seen only asfragments.

c. Oval, biconvex, more or less polyhedral, or irregularlyshaped cells, consisting of a relatively opaque, or whatappears as a granular cell-substance, and including an excen-tric large oval nucleus of the same aspect and size as that of

1 I may here mention that I know of no better reagent for the demon-stration of goblet-cells than 5 per cent, chromate of ammonia, A piece oftrachea of a mammalian animal placed fresh in 5 per cent, chromate ofammonia, kept there for twenty-four hours, and treated in the manner abovedetailed, yields excellent specimens for the study and demonstration ofgoblet-cells in all different stages between ordinary normal epithelial cellsand bulky goblet-shaped mucus-containing cells.

326 DR. E. KLEIN.

the preceding cells. They are met with isolated orin groups;in the latter case they are likewise imbricated and form thewall of gland-tubes, somewhat narrower than those men-tioned siib b. Both are sections of the same gland-tube: thebroader, lined by the transparent flat cells, appear to be themore superficial, the narrower lined by non-granular cells,the deeper portion of the stomach glands.

d. Exceedingly large transparent placoids, with an ovalnucleus in the centre j they arc met with relatively rarely,and only in preparations which were made with a view of in-cluding in the scraped flakes the tissue of the deeper parts ofthe mucosa. When looked at in profile they appear more orless spindle-shaped, the cell-substance appearing at eachpole of the nucleus as along filamentous prolongation. Thenucleus of these endothelial plates—for such they are in allprobability—resembles in aspect and size perfectly that ofthe flattened transparent gland-cells ; the intranuclear net-work presents itself in great clearness. Fragments of theendothelial plates cannot be, therefore, distinguished fromthose gland-cells.

As regards the epithelial cells mentioned sub a, it is afact too conspicuous to be overlooked, even under a moderatelyhigh power (e. g. about 300), that the substance of the uppertransparent, as ivellas the lower or opaque part of the goblet-cells contains a great number of delicate fibrils, more orless distinctly stained, many parallel to the longitudinalaxis of the cell. They are especially distinct in the upperor transparent part of the goblet-cell. These fibrils can,in many cells, be traced up to the free margin of the goblet,i. e. the margin of the cell which, as has been mentionedabove, has lost its cover; they anastomose with each otherby lateral branchlets. If such a cell is looked at along itslongitudinal axis these lateral branchlets are not very conspi-cuous, but in an oblique, or, still better, in a bird's-eye view,we obtain a clear insight into their arrangement, and wethus convince ourselves that the longitudinal fibrils and theirlateral branchlets form a very delicate and more or less densenetwork. This network we shall designate the intracelhdarnetwork ; it is represented in figs. 1, 2, 4, 5. That this net-xoorli of the intracellular fibrils comes out with such dis-tinctness in these goblet-cells is no doubt due to the inter-

fibrillar or ground-substance having swollen up vpry much ;by doing this the meshes of the network become of coursedistended, and, therefore, distinctly perceptible.

The ground-substance or interfibrillar substance of thesegoblet-cells is mucin, and it stains in a characteristic

OBSEH.VATIONS ON STRUCTURE OF CELLS AND NUCLEI. 3 2 7

manner deeply blue with haematoxylin. This is the reasonwhy hsematoxylin-staining does not yield such clear views ofthe intranuclear, and especially the intracellular network offibrils, as carmine or picrocarinine, viz. because hsematoxylinstains the ground-substance of the cell too deeply, on accountof its containing mucin, and thereby these networks becomemore or less obscured, whereas carmine or picrocarmineleaves the ground-substance transparent and unstained, butstains both the intracelltilar and intranuclear network.

The intracellular fibrils and their network is best seenin the slender goblet-cells of stomach (of newt) keptfor twenty-four hours in Miiller's fluid, placed then forabout half an hour in a mixture of two parts of chromicacid (^ per cent.) and one part methylated alcohol, washedafter this in water, and stained in picrocarmine. The fibrilsrunning in the long axis of the cell come out with remark-able clearness; if the upper part of the cell is inspected inan oblique manner it is seen that the fibrils form a densenetwork. In fig. 12 I have faithfully represented two suchcells.

In the epithelial cells of the foregut that have retainedtheir cilia we recognise in the last-named specimens withgreat clearness that the cilia pass into the cell-substancethrough the cell-cover—hence the striated or granular ap-pearance of this latter—and indentify themseloet with theintracellular network of fibrils. Ebtrth, Marchi,1 and especiallyEimer2 have noticed a similar condition.

Another point not less conspicuous, is the direct connectionof the fibrils of the intracellular with those of the intra-nuclear network. In our preparations with 5 per cent,chromate of ammonia this connection of the intranuclear net-work, both with the fibrils of the upper and lower portion ofthe cell, is much more distinct than in specimens preparedwith Miiller's fluid, on account of the intranuclear networkbeing more clearly perceptible in the former than in thelatter.

What I have stated with reference to the structure of theepithelial cells mentioned sub a, applies likewise to thosementioned sub b, c, and d, viz. that we have to distinguishin the cell-substance two parts, one the homogeneousground-substance and the other the intracellular network offibrils. This latter is in direct anatomical continuity withthe intranuclear network. But there exists a difference inthe density of the intracellular network between the different

1 'Archiv. f. Mikr. Auat.,' Bd. iv.5 1,. c, p. 115, figs. 3, 11, 20, and 21.

VOL. XVIII. NEW SKR. ' Y

328 DR. E. KLEIN.

cells; for those sub c mentioned, viz. the opaque or 'dis-tinctly granular' gland-cells situated in the deeper parts ofthe gland-tubes contain a very dense network of fibrils, andof course little of the interfibrillar ground-substance is seen,hence the ' granular' aspect of these cells. I have repre-sented such a cell in fig. 7. In the flattened gland-cells de-scribed sub b and the endothelial plates, sub d, the hyalineground-substance forms a formidable portion, the intracelltilarfibrils forming a network with relatively wide meshes ; lookedat from the broad surface the cell-plate presents longitudinalfibrils, in some places placed more closely than in others, andanastomosing by lateral branchlets. When seen in profilethe continuity between the intracellalur and intranuclearnetwork is very distinct (figs. 9, 10, and 11).

B The mesentery of a freshly killed newt (the black species)is cutout together with the intestines and placed in a solutionof 5 per cent, chromate of ammonia, where it remains fortwenty-four hours; it is then carefully cut into several portionswhile under water, then cut off the intestine and left in waterfor about \—1 hour ; after being stained in carmine, or picro-carmine, or heematoxjlin, it is ready for microscopic examina-tion. For this purpose one or the other portion is floatedon an object-glass, and after having being spread out it iscovered with a covering-glass, a drop of glycerine havingpreviously been placed on the latter. It is necessary thatthe preparation should be well spread out, but should notbe subjected to any undue pulling or other mechanicalinjury, for this does invariably annihilate many of thoseexquisitely delicate structural peculiarities that I am goingto describe below. But I must add that it requires notmuch more than ordinary delicacy of handling in order toobtain success, and I will likewise add that I know of nomore beautiful object in histology than a preparation of themesentery of newt prepared in the above manner, well stainedwith hsemaxotylin or doubly stained with picrocarmine firstand hsematoxylin afterwards and well spread out. Mountedin glycerine the preparations preserve all their fine qualities.

In our specimens we have to notice the following struc-tures:—(1) the endothelium of the surface,(2) the ground sub-stance, (3) unstriped muscle-fibres (4) connective-tissuecorpuscles, (5) bloocl-vessels, and (6) nerve-fibres.

I. Endothelium of the surface.In our specimens we find the endothelium of the surface,

when not detached from the subjacent membrane, repre-sented as a transparent hyaline layer containing large


oval nuclei at more or less regular intervals. The nucleimeasure in the mean 0-018 by 0-014 mm., and show in allinstances an exquisitely pretty network uniformly pervadingtheir interior. This intranuclear network possesses the samecharacters as that described of the cells of the stomach. Thenetwork varies in form and arrangement between that of adelicate net and that of a honeycomb of a sponge ; the brightdots to be observed in it correspond mostly to fibrils seen inoptical section. There are no structures comparable tothe nucleolus. In some parts of the specimen we findthe endothelial membrane of the surface broken up intoisolated plates corresponding to the individual endothelialcells, or into smaller groups—two or three—of them.The isolated endothelial cells show generally a singleexcentric nucleus—in exceptional instances the nucleus isdouble—and are in many instances more or less folded or rolledup. If we get the endothelial plates in our specimen clear ofthe membrane of the mesentery and unfolded we notice thattheir substance shows a beautiful network of fibrils, such as Iattempted but only imperfectly succeeded to delineate infigs. 13, 14, and 15 ; in the drawings the network is com-posed of far too coarse fibrils. The fibrils are exceedinglydelicate, run in bundles which anastomose and thus form afenestration with large or smaller fenestrae. At first sight,and looked at with only a moderately high power they(fibrils) seem to be only streaks of a ' granular substance.'That this latter is composed of fibrils becomes clear whenexamined more carefully and with a higher power, such asZeiss F , or Hartnack Irnm. 10. Thus we have to distinguishalso in the endothelial plates a hyaline ground-substance,which I wish to call ground-plate, and in it a network offibrils—the intracellular network. Thus network is in allendothelial cells of our specimens in direct communicationwith the intranuclear network (see figs. 13, 14, and 15.) Ingroups of endothelial plates not showing the outlines of theindividual cell-plates we notice that the intracellular fibrilsof one plate merge into those of its neighbours, apparentlywithout any distinct interruption.

Schwalbe1 describes each of the endothelial cells liningthe canal of Schletnm as consisting of a hyaline, delicateplate, with an oval nucleus and 'reticular thickenings;' infigs. 30 and 31 accompanying his paper this arrangementis well shown on isolated endothelial plates prepared inMiiller's fluid. 1 have no doubt that these ' reticular thick-

1 " Unters. iiber d. Lymphbahnen d. Auges," &c, ' Archiv. f. Mikr.Anatom.,' Bd. vi, p. 305.

330 DR. E. KLEIN.

eniiigs' are not in reality thickenings of the endothelialcells, but correspond to our intracellular network of fibrils.

Tourneux1 asserts that the endothelium lining the peri-toneal surface of the septum cysternse lymphaticee magnse ofbatrachian animals consists of two superimposed strataof cells, a superficial one composed of a single layer ofhyaline, thin, non-protoplasmic plates, with or without anucleus, and a deep layer of protoplasmic cells. Tourneuxthinks that the superficial cells become detached after theyhave lost their nucleus, and that the lower protoplasmic cellsby division produce their substitutes.

v. Ewetsky2 maintains of the endothelium of the mem-brana Descemeti of frog, pigeon, cat and calf, that its cellsconsist of a hyaline membrane and a subjacent nucleated,branched, protoplasmic corpuscle.

I have little hesitation in saying that the hyaline plateof Tourneux and Ewetsky correspond to our ground-plate,and that their subjacent protoplasmic corpuscle is identicalwith our intracellular network in connection with the nucleus.Contrary to these observers I regard both the ground-plateand intracellular network as forming one individual endo-thelial plate, that is to say, the intracellular networkconnected with the intranuclear network lies embedded inthe hyaline ground-plate.

II. The ground-substance of the mesentery is a delicateconnective-tissue membrane, being composed of a feltworkof very fine fibrous bundles, to which are added the ordinaryfine elastic fibrils branching and anastomosing. But thisground-substance is in our specimens, in which the otherelements are shown with all clearness of detail, only veryfaint.

III. The unstriped muscle-fibres.The mesentery of the newt contains a very beautiful

plexusof unstriped muscle-fibres. They are arranged3 in flatbundles, crossing each other, but chiefly interchanging itsfibres. The bundles are made up of a limited number offibrils, ranging between ten or more abreast down to slenderbundles of three or two fibrils. Most of the unstripedmuscle-fibres are included in this plexus, but there areindividual and couples of fibres leaving this plexus and

1 " Recherches sur l'epith. des Sereuses," ' Journ. de l'anatoraie et de laphysiologic,' Jan. et Fev., 1874.

3 " Uber d. Endothel. d. Membr. Descemeti," ' Untersuch. aus d. path.Inat. Zurich.,' iii, 1875.

* The description given here refers to specimens that have been wellspread out. The arrangement naturally differs if the specimens are in amore or less shrunken condition.


terminating freely in the ground-substance of the mesen-tery. Whether the bundles be large or small, the indi-vidual fibres are sufficiently separate from each other as toallow their examination in all parts. Of great beauty arethose parts of our specimens in which the minute bundlesare composed of a limited number of fibres (two—five), andwhen they freely intercommunicate with each other.

Most of the muscle-fibres remain undivided, and terminateat each extremity in one single pointed end; there are, how-ever, such as divide close at the nucleus or at a part notdistant from it into two, seldom into three, branches.

The nucleus of the muscle-fibres is oval and slightlyflattened; when seen in profile it measures in the mean0*027 mm. in the long, 0*008 mm. in the transverse,diameter. The nucleus lies not exactly in the middle of thelong diameter of the muscle-fibre, but not very far from it,as the following measurements show :

In muscle-fibre (a), O'SOC mm. from middle of nucleus to the corre-sponding extremity of the muscle-fibre.

0'294 mm. the rest.In muscle-fibre (b), 0282 mm. from middle of nucleus to the corre-

sponding extremity of the muscle-fibre.0"354 mm. the rest.

The length of the thin examples is about 0"61 mm.; butthere are others which are shorter, being much thicker.

As I have mentioned above, the muscle-fibres are, in speci-mens that have been well spread out, so much separated fromeach other that they can be easily followed from one endto the other3 and it is thus a matter of great facility inseeing that most fibres are more or less wavy and curved,and that some possess from place to place varicose swellings.Examining these varicosities with a high power we observethat they are composed of two substances:—(1) a sheathcontaining transversely arranged thickenings in the formof annular markings, such as represented in fig. 17 e, and(2) a. central bundle of fibrils;1 the thickness of this bundlevaries naturally according to the thickness of the pointexamined, i.e. whether a part near the extremity or thenucleus (i.e. near the thick part) of the muscle-fibre, but isalways slightly thicker corresponding to a varicosity than inthe parts between.

1 That the substance of unstriped muscle-fibres in general is longitudinallystriated, i.e. probably composed of longitudinal fibrils, has been known toliistologists for some time (Arnold, ' Strieker's Manual of Histology,1 chapteron unstriped muscle; E- Klein, 'Handbook of the Physiol. Laboratory,'edited by Dr. Burdon-Sandersou, chapter on unstriped muscle tissue, tig.07 of plate xxv; W. Flemming, I. c, p. 714).

332 DR. E. KLEIN.

The same distinction into a sheath and a central bundleof fibrils exists also in the part between two varicosities,with this difference, that the sheath is thinner and the annu-lar thickenings are scarcer and not so distinct. Those fibreswhich in a greater portion, especially next the nucleus, donot possess any varicosities, exhibit the transverse rings ofthe sheath with great uniformity. When looked at in pro-file this appearance is in some respects similar to that ofmedullated nerve fibres (Lantermann, MacCarthy), and espe-cially of preparations of nerves prepared with chromate ofammonia, as described by MacCarthy (1. c.) But in ourmuscle-fibres the transverse markings being due to ringsmay be followed over the upper as well as lower surface ofthe fibre, which of course is not the case in the medullatednerve-fibre where those markings are due to rods placed ver-tically to the long axis of the fibre.

fin fig. 17, a and b, the muscle-fibres have not been represented in theirwhole length, as this would have occupied too great a space, and thereforethe varicosities which are especially distinct, and sometimes of a veryregular distribution near the extremities of the fibre, are not shown suffi-ciently numerous.]

The sheath with its transverse markings is visible alsoon the thickest part of the muscle-fibre, i.e. the part thatincludes the oval nucleus. For the demonstration of thetransverse markings all specimens are useful, haematoxylinspecimens, however, being best. The distinction between asheath with annular thickenings and a central bundle offibrils, is shown with remarkable clearness in some muscle-fibres in which that bundle had shrunk avvay from the sheath,and thus presents itself as a wavy or more or less zigzaggroup of fibrils within the latter. In the accoinpanyingwoodcut (b)} a portion of such a muscle-fibre is shown.

Within the limiting membrane of the nucleus of everymuscle-fibre we notice the very distinct intranuclear networkof fibrils. This network is stained in our specimens, whereasthe ground-substance is in most instances quite transparentand unstained ; in a few instances- I have seen it, however,assuming a slight tint. There are muscle-fibres to be met withwhich, instead of a single oval, possess a constricted nucleus,the constriction being placed either transversely or, more

OBSERVATIONS ON STRUCTURE OF CELLS ANT) NUCLEI. 3 3 3

usually longitudinally. In such a nucleus we notice that thisintranuclear network forms two distinct groups—one for eachpart of the nucleus—connected with each other by parallelthreads. There are nuclei possessed of one or two smalleror larger rounded buds; these contain a small network con-nected with the bulk of the intranuclear network by a fewsmall threads. This is shown in b, of the accompanyingwoodcut.

It is probable, from this, that the division and multiplica-tion of the nucleus of unstriped muscle-fibres is precededby a process of gemmation. In. most muscle-fibres thenucleus is seen in profile, and the bulk of the intranuclearnetwork occupies an axial position; from it pass numeroustransverse fibrils towards the sides of the nucleus.

In all muscle-fibres the intranuclear Jibrils may be tracedto emerge as a bundle from the pole of the nucleus, and tobecome identified with the bundle of fibrils representingthe core of the muscle-fibre itself. This point, viz. the con-nection of the intranuclear network with the bundle offibrils of the muscular substance is shown well enough inpreparations stained with haematoxylin, but it is perhapsstill better shown in parts of mesentery stained first withpicrocarmine and then with haematoxylin. In a muscle-fibre which, close to the nucleus, divides into two processeslike the one represented in fig. 17, e, we observe that theintranuclear network sends forth two bundles of fibrils,one for each division.

A very interesting relation that I have been able to ascer-tain in some nuclei, is ihis: the nucleus possesses asmall circular opening at each pole, through which the bundleof fibrils emerges. (I have tried to represent this in fig.17, d, but fear not with great success). The same relationprobably exists in all fibres.

Thus, we may regard the unstriped muscle-fibre as com-posed of a sheath with annular thickenings, and a bundleof delicate fibrils which at one more or less central pointforms a delicate network; this surrounded by a specialmembrane—except where the network is in connection withthe bundle of fibrils—represent the nucleus.

I am unable to say what the nature of that sheath is,but I think it is probably of the nature of an elasticsheath, and I can well understand its importance in thefunction of the muscle-fibre. The central bundle of fibrilshaving its fixed point, as it were, in the intranuclear network,shortens during contraction towards this, and is brought backagain into its conditioxi of rest by the elasticity of the sheath.

334 DR. E. KLEIN.

The above-named varicosities and the different conditionof the sheath and central bundle in the varicose and inter-varicous portions bear a very strong support to this view; forthe varicosities are in all probability portions of the muscle-fibre in a state of contraction, and hence the narrownessof the transverse rings, the thickness of the sheath, and thebreadth of the central bundle of fibrils. Another point whichcan be, 1 think, only interpreted in the sense of this theory,is the fact that in the thicker muscle-fibres we find thesheath thicker and the annular markings much closer andmore numerous thau iu the thinner examples.

As a last fact of some interest may be mentioned the ter-mination of these muscle-fibres. I have noticed in a fewinstances that the extreme end does not terminate in a freepoint, but is either at or near this in connection with the

fine processes of a connective-tissue corpuscle.

IV. The connective-tissue corpuscles.a. The migratory cells are in some parts more numerous

than in others, but they are to be met with in almost allportions of the mesentery. Most of them are possessed ofcoarse granules and are of various shapes—elongated, con-stricted, irregular, and possessed of knob-like prominences.Their nucleus is generally single, oval and large, or in someinstances constricted, but in all cases it shows a beautifulintranuclear network (see figs. 20 and 21). Iu some of thesecells the nucleus as a whole is more deeply stained (iu car-mine as well as in hsemaioxylin) than in others, and I con-clude that the ground-substance of the nucleus is iu theseinstances of a different nature, the whole cell being younger.A minority of migratory cells possess a pale, slightly andindistinctly fibrillar substance surrounding the relativelylarge nucleus, and a few knoblike or filamentousprocesses. The nucleus of these cells shows the net-work of fibrils with equal distinctness. Also in the nucleiof many of these cells we find the ground-substance of thenucleus staining a deep tint.

b. The connective-tissue corpuscles proper or fixed cellspresent themselves in great delicacy and beauty, both in speci-mpiis stained in picrocarmine as well as hsematoxylin. Whatattracts our attention in the first instance is the remarkabledistinction between a hyaline, slightly but distinctly tintedground-plate and the fibrillar substance or intracellular net-work of fibrils, which forms a collection round the nucleusand is prolonged beyond the. ground-plate in numerous richlybranched processes,, which in some instances form a con-


tinuous network with those of neighbouring cells. Thenucleus is oval, and measures about 0"013 by O'Oll mm.;it contains a very beautiful and delicate network of fibrils;these pass through the nuclear limiting membraue into thefibrillar substance of the cell, with which they becomeidentified.

(a) The intranuclear network stains well and contains hereas well as in those of the cells of other kinds, previouslynamed, bright dots, owing to the fibrils being looked atin their optical transverse section or at their point of anasto-mosis, and larger irregular particles—thickened or con-tracted (shrunk) portions of the network. I have seennuclei whose network had so much shrunk as to form acentral irregular mass, in which the individual fibrils couldbe distinguished only with difficulty. There could be nodoubt as to its nature, although at first it resembled in ahigh degree what corresponds to the ' nucleolus ' of theauthors. In these instances, therefore, I see additionalevidence for the correctness of the view first expressed byLanghaus (I.e.), viz. that the nucleoli owe their origin,probably in most instances, to the shrunk condition of theintranuclear network. The nuclear membrane shows inthose instances in which the network is not shrunk toomuch, besides the faint outline representing the limitingparts of the network, in addition a thicker boundary,such as had been mentioned to exist in the nuclei of theepithelial cells of stomach.

Q3) The fibrillar substance or intracellular network isarranged round the nucleus in a very unequal manner, suchas is represented in fig. 23, and it is in this part especially,and also in the thicker prolongations of it, that the characterof a fibrillar network can be made out most distinctly. It ispossessed of numerous processes unequal in thickness andlength; they are all very richly branched. Of characteristicappearance are the irregular thickenings in the course of theprocesses and the club—or pear-shaped prolongations at thepoint of branching of these processes.

The branching of the processes is very rich; the anasto-mosis of processes of neighbouring cells is rarer than itwould appear at first sight. Only in rare instances have Iseen an anastomosis of two processes coming out of the samecell. In many cases the processes terminate either club-shaped or in the form of an irregular plate. I need hardlysay that in this description of connective tissue corpuscles Irefer to specimens or parls of them in which the endothelialcovering of the surface has become over larger or smaller

336 DR. E. KLEIN.

arese loosened and detached, but the elements of the tissue :such as unstriped simple fibres, connective-tissue cells, nerve-fibres and capillary blood-vessels, remained undisturbed,presenting all details of structure. The same details may beof course also seen where the endotheliuni of the surface hasretained its position, only for obvious reasons it requires amore attentive examination.

(-y) The ground-plate is faintly stained and therefore notwell defined in all parts of its outline. Although thegreater number of processes of the fibrillar substance—except the thicker branches—pass beyond the limits of theground-plate, still there are some minute processes whichremain within its area. I find a good many instances inwhich I can trace fibrils coming out of the nucleus andrunning up to the margin of the ground-plate, where theyterminate. These fibrils, which appear to connect the nucleusdirectly to the edge of the ground-plate, are not representedspecially in fig. 23, but they are very clear in many con-nective-tissue corpuscles. An inspection of fig. 23 no doubtsuggests to the reader—as a cursory inspection of thespecimens would to the observer—that, supposing the ground-plate be not visible, the rest of the connective-tissue cor-puscle corresponds to those typical branched connective-tissue cells as they usually present themselves, viz. an ovalnucleus unequally surrounded by the ' granular' cell-substance, which is drawn out into more or less branchedprocesses.

I shall have occasion to return to this question of thenature of connective-tissue corpuscles in the second part ofthis memoir, when I shall be able to discuss it in connectionwith the cells of tendon, cornea and loose connective tissue,and when I shall be able to examine critically the assertionsand observations of various writers, especially v. Reckling-hausen, Strieker, Rollett, Schweigger-Seidel, Schwalbe, Boll,Waldeyer, lianvier, Griinhagen, Eberth, Ewetsky, Bbttcher,JBizzozero, Waller, Lavdovski, Axel Key, Eetzius, Spina,JRenaut, but this much I may say here that the two sub-stances, viz, ground-plate and fibrillar substance connectedwith the intranuclear network of the oval nucleus form theessential parts of a connective-tissue cell. It is to me clearthat in the case of the connective-tissue cells of the mesenterythe two parts are not merely superimposed, but form oneintegral element in the same manner as I stated it to bethp case with the endothelial cells of the surface.

V. T/te blood-vessels and lymphatics.In all blood vessels of our specimens we recognise the net-


worh in the nuclei. This is of course best shown in capillaryblood-vessels, on account of the thinness and transparencyof the wall. In some capillary vessels, when looking at thewall from the surface, I have noticed from place to placefragments of a minute network ; it is quite possible that theseplaces correspond to the granular substance observed some-times in the endothelial plates constituting the wall of thecapillary. Some such capillaries contained blood-corpuscles ;and the nuclei of these showed a very distinct network. I havebeen able to recognise in some specimens apparently ceecaldilatations of lymphatics, the nuclei of the endothelial wallof which whether looked at from their broad or narrow sidepresented the intranuclear network with great distinctness,and in all respects similar to that described of the othernuclei. Also the nuclei of lymph-corpuscles present in thelymphatic exhibited a network of fibrils (see fig. 22).

VI. Th", nerve-fibres.Without wishing to enter here into a description of the

distribution of nerve-fibres in the mesentery,1 I have onlyto mention the extremely long, more or less wavy and curvedcourse the fine nerve-fibres pursue without giving off anybranches. Each such nerve represents a bundle of finefibrils, i.e. an axis cylinder, to which is applied from placeto place an oblong constricted or slightly folded nucleus.The number of nuclei along such an axis cylinder depends onthe thickness of this latter. I measure, as far as this is pos-sible in a fibre presenting a number of curvatures, threesuccessive segments from nucleus to nucleus, in fibre(«): 0-1, 0-16, 0-128 mm. ; in fibre (b): 016, 0-208,014 mm. But in what appear to be the thinnest fibresthe length of a section between two nuclei reaches about 0'75of a millemetre.

The nuclei are oblong and slightly flattened; their out-line is not smooth, but is wavy or notched in, and thereforelooks as if folded. The mean size of such a nucleus is0026 by 0006 or 0'008 mm.; its outline, however, oncareful inspection is not very well defined, especially corre-sponding to its poles we miss in many instances the limitingmembrane. Each nucleus is embedded in a hyaline platefolded over the bundle of fibrils representing the nerve-fibre; this plate—ground-plate we will call it—is very wellshown in specimens stained in haematoxylin, or doubly

1 I have described minutely the distribution of fine nerves in themesentery of frog in this Journal, Vol. XII, 1871; the minute nervesbelonging to the ground-substance of the mesentery appear to be far lessinumerous in the newt Llia.ii in the frog.

338 DR. E. KLEIN.

stained in picrocarmine and hsematoxylin, as it assumesa distinct tint. As shown in fig. 23, b, it extends a certaindistance beyond the poles of the nucleus. In some places theexpansion of the ground plate is much greater at one side ofthe nucleus than at the other. To each nucleus, therefore,corresponds a cell-plate, and consequently we find a greaternumber of cell-plates, the thicker the nerve-fibres. Amicroscopic nerve trunk of the mesentery of batrachianand other animals exhibits, by the aid of silver-staining, thepresence of a complete envelope of nucleated eudothelialplates. (Axel Key and Retains, Ranvier.)

The nucleus contains in all instances a beautiful networkof fibrils, and in this respect it is second to no nucleus ofany other kind.

A point that deserves careful consideration is the relationof the fibre-bundle, i.e. the axis cylinder, to the intranuclearnetwork. I have examined the nerve fibres in my specimenswith great attention, and I have failed to obtain any evidenceof a connection of the two; on the contrary, in most in-stances I am able to follow the axis cylinder along one orthe other side of the nucleus beyond this latter, and thereis every reason to regard this condition as the rule. If inan isolated instance the appearances are against it, I caneasily account for it. The reason is this : the nucleatedcell-plate, which at intervals ensheathes the axis cylinder,does not consist merely of the hyaline ground- plate and nu-cleus, as mentioned above, but possesses fibres, which I willcall investing fibres ; they are in connection with the intranu-clear network, and pass beyond the ground-plate, they followclosely the axis cylinder and appear to be twisted round, it soas to actasa the sheath for the sections between two neigh-bouring cell-plates. If, then, in one or the other instance itwould appear as if the axis cylinder were in connectionwith the intranuclear network, these investing fibres mustnot be forgotten. I have not represented these fibres infigure 23, because they were not distinctly differentiated inthe nerve-fibre delineated in this figure, which is a faithfulrendering of the appearances observed in this particularnerve-fibre; but there are others in which 1 have seen theinvesting fibres with sufficient distinctness. Thus, thereexists a complete aualogy between these cell-plates and theconnective-tissue corpuscles described in a former paragraph,for in both we distinguish a hyaline ground-plate from thefibres which, on the one hand, are in connection with the in-tranuclear network, and, on the other hand, pass us the pro-cesses beyond the limits of the ground-plate. The difference

OBSEUVATIONS ON STRUCTURE Of CELLS AND NUCLEI. 3 3 9

between the two kinds of cells lies merely in the distributionand amount of these fibres; in the connective-tissue cellsof the mesentery of newt the fibrillar substance forms aconsiderable portion of the whole cell, being present in a per-ceptible amount around the nucleus and extending fromhere in all directions as the branched processes : in the cell-plates of the nerve-fibres, on the other hand, there is noappreciable collection of that substance around the nucleus,and the fibres extend apparently only in the two opposite,or at most three directions. This last fact is easily accountedfor, considering that thi! cell-plate of the nerve-fibre isdoubled round this latter, and consequently must be withoutprocesses at least on one side, .ie., the margin of the fold.

It is easily understood that the intranuclear network ofthe cell-plate of a nerve-fibre is in connection with the pro-cesses and intranuclear network of a Tieighbouring connective-tissue corpuscle—a fact which I observed in the instancefigured in 23 of Plate XVI.

It is not at all improbable that tbe assertions of a connec-tion of minute nerve-fibres with the processes of connective-tissue corpuscles—'too well known in the literature of thecornea—are to be explained in this manner.

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