10 GENERAL ANATOMY OF THE TISSUES. 



fluid are rare, (fat-cells, blood-cells, cells of the chorda 

 dorsalis), and it is colourless or reddish ; in general they 

 contain, in addition, corpuscles in greater or less number, 

 (elementary granules, elementary vesicles, perhaps crystals), 

 and in fact, as a rule, young cells possess few, while older 

 ones contain many, which are very often more densely grouped 

 round the nucleus, or occupy only a single spot (coloured 

 nerve-cells). 



The chemical composition of the cells is as yet very obscure. 

 The contents in most cells present certain generally disseminated 

 substances, which occur dissolved in the nutritive fluid or 

 cytoblastema, as water, albumen, fat, extractive matter, salts ; 

 a nitrogenous substance, which is precipitated by water and by 

 dilute acids thus resembling mucus, is very extensively dis- 

 tributed and considerably impedes the microscopical analysis 

 of the cells and tissues, inasmuch as it causes them to be 

 obscure and granular, instead of clear and transparent. Many 

 cells contain yet other compounds, as those of the liver, of 

 the kidneys, of the blood, &c. The cell membrane consists of 

 a nitrogenous substance, which is unquestionably a protein 

 compound in young cells, as we may conclude from its solubility 

 in acetic acid (partly even in the cold) and in dilute caustic 

 alkalies. Subsequently the membrane in many cells, yet by 

 no means in all, (e. g. not in the blood-corpuscles, in the 

 deepest cells of the epidermis and epithelium, nor in the cells 

 of the glandular follicles), becomes less soluble, and here and 

 there more or less approximates the substance of the elastic 

 tissue. 



The celUnucleus is a globular or lenticular, clear, or 

 vellowish bodv, which in the mean measures 0-002 — 0004'", 

 and rarely, as in the ganglion-globules and ova, attains a 

 diameter of 001 — 0'04'". All nuclei are vesicles, as Schwann 

 supposed and as I have recognised to be their original and 

 universal structure in embryos and adult animals. The mem- 

 brane is very delicate in the smaller ones, appearing as a 

 simple, fine, dark line ; in the larger it is more marked, even 

 of measurable thickness and limited bv a double contour, 

 as in the nuclei of the ganglion-gloDules, of ova and of many 

 embryos. The contents of the nuclear vesicle consist, ex- 

 cepting the nucleolus, almost invariably of a pellucid or slightly 



