SURVEY OF CELL-LIFE. 181 



of the original cell is retained (independent cells), or as it is 

 more or less completely lost (coalescing cells, and cells which 

 undergo division). 



The varieties which occur amongst the independent cells, are 

 partly of a chemical nature, and partly have reference to a dif- 

 ference in the growth of the cell-membrane, by which means 

 a change in the form of the cell may be produced. 



The cell-membrane differs in respect to its chemical quali- 

 ties in different kinds of cells. That of the blood-corpuscles, 

 for instance, is dissolved by acetic acid, whilst that of the 

 cartilage-cell is not. The chemical composition of the cell- 

 membrane differs even in the same cell according to its age, 

 so that a transformation of the substance of the membrane 

 itself takes place in plants ; for, according to Schleiden, the 

 cell-membrane of the youngest cells dissolves in water, the 

 fully-developed cells not being acted upon by that fluid. The 

 simple cells are still more remarkable for their cell-contents. 

 One cell forms fat, another pigment, a third etherial oil ; and 

 here also a transformation of the cell-contents takes place. A 

 granulous precipitate is seen to form gradually in what was in 

 the first instance a pellucid cell, and this usually takes place first 

 around the cell-nucleus ; or, vice versa, during incubation, the 

 granulous (fatty) contents of the cells of the yelk-substance 

 gradually undergo partial solution. According to Schleiden, 

 this transformation of the substance of the cell-contents pro- 

 ceeds in accordance with a certain rule ; I have not made any 

 investigations upon the subject in animals. 



We should also include under this head the formation of 

 the secondary deposits upon the internal surface of the cell- 

 membrane, so very frequently met with in plants. If a firm 

 cohering substance be formed from the cell-contents, it may 

 be deposited upon the internal surface of the cell-membrane. 

 In plants this deposition generally takes place in la vers, a 

 stratum being formed in the first instance upon the internal 

 surface of the cell-membrane, upon the internal surface of 

 that one a second, and so on until at last the entire cavity 

 may be almost filled by them. According to Valentin, these 

 surrounding deposits always take place in spiral lines which 

 are subject to great varieties in their arrangement, for there 

 may be one or many of them, and they may cither completely 



