CELLS. 65 



The nuclei also occasionally, though upon the uholc rarely, take part 

 in the changes of the cells. The commonest of these appearances is 

 their becoming clear, as a consequence of the liquefaction of the at first 

 more viscid contents, upon which circumstance it depends that in 3'oung 

 cells they are homogeneous, while in the larger they evidently appear to 

 be vesicles. A formation of granules in the nuclei is very rare (see 

 above) ; concretions, coloring matters, and crystals, are also not found 

 here in animals ; on the other hand, the development of the urticating 

 threads in certain animals and that of the spermatozoa, takes place in 

 nuclei. 



In endeavoring to explain the metabolic processes of cells, we must 

 in all cases especially regard the cell-nucleus ; for just as it excites the 

 development of the cell, so is it the centre of the currents of the contents, 

 and of the deposits and solutions ; but it is not to be regarded as tire 

 sole agent, for, firstly, it does not appear why the cell-contents should 

 not, like the cytoblastema, become changed of themselves ; and, secondly, 

 the changes of the cell-membrane are, at all events, more independent, 

 and probably also have a certain influence upon the cell-contents, as 

 the depositions which take place upon it, and the solution of the solid 

 contents which often occurs in its neighborhood, demonstrate. To 

 assume with Schwann a special metabolic force is incorrect, for, in the 

 first place, the causes of the metabolic phenomena are certainly very 

 various ; and, secondly, there is every reason to reduce them to known 

 molecular forces. Thus, for instance, even the action of the nucleus* 

 may not unfittingly be compared with the so-called catalytic, or contact 

 action, inasmuch as it is hardly at all altered during the changes of the 

 cells, and consists of a nitrogenous substance, which like pepsin (which 

 is also nothing but cell-contents), very readily produces a chemical altera- 

 tion in other substances. The relation of the cell-membrane to absorp- 

 tion also, may even now be referred to the general laws of imbibition 

 and difi"usion. 



I here give two analyses as examples of the chemical composition of 

 the cell-contents. The yelk of the hen's egg contains: water, 48*55; 

 casein, 13-93; albumen, mixed with casein, 0-892; albumen, 2-841; 

 membranes of the yelk vesicles, 0-459 ; fats, 81"146 (30-46 according 

 to Gobley), consisting of olein and margarin; 21*304; cholesterine, 

 0*438 ; lecithin (containing phosphoric acid), 8*426 ; and cerebrin ; salts, 

 1*523; a hundred parts of the ash yielded, potass, 8-60-8-93 ; chloride 

 of sodium, 9*12 ; phosphatic salts, 06*7-67-8 ; lime, 12-21 ; magnesia, 

 2-07; oxide of iron, 1-45; silica, 0-055. The blood-corpuscles contain: 



* [This "adton of nucleus" is a wholly hypothetical though a very general assumption 

 It is important to bear in mind, on the contrary, that there is every reason to believe that 

 the molecular and chemical changes of the cell-membrane and the nucleus are independent 

 of one another. — Tks.] 



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