POST-MORTEM CHANGES OF CELLS. 45 



germinal membrane. Moreover, all cutaneous glands would 

 have to be included in the series of epidermal cells, all epithelia 

 in the series of secretory cells, and, lastly, connective tissue, 

 muscle, and blood would require to be combined in one and 

 the same category. If no objection can be raised to many 

 of these systems of arrangement, it is at least impossible to 

 regard any of them as perfect. 



Morphological peculiarities alone constitute a ground for the 

 formation of subdivisions, and these will be considered in 

 subsequent chapters, 



FORMATIVE ACTIVITY OF CELLS. The recognition of the 

 fact that the animal body, excluding the ingesta, consists only 

 of cells, or of cell derivatives, constitutes one of the most valu- 

 able conclusions arrived at by Schwann. 



The next chapter will place before the reader, in a more 

 extended form, the facts on which he grounded this statement. 

 We can here only refer to the general importance of cells in 

 the animal body, and in regard to their formative activity it 

 may suffice to point out that every organised portion of the 

 animal body which is not a cell must originate in or from cells. 

 In addition ijp the organised constituents of the animal body, 

 chemical compounds are also present in it, which, so far as they 

 have not been introduced in those forms, must be regarded as 

 the products of cell activity; but we cannot ascribe the non- 

 organised bodies, even though they may be deposited as solid 

 compounds, to the formative activity of cells. To this account 

 we only place those materials which become a portion of the 

 organised constituents of the animal body through cell meta- 

 morphosis. 



CHANGES OF CELLS IN DEATH. It is difficult in many cases 

 to decide whether a cell still lives ; it is not sufficient to know 

 that the preparation has been taken from a living animal, or 

 from the body of one which has only been dead for some hours. 

 If the cells exhibit no amoeboid movement, and if, on the other 

 hand, they are not taken from putrefying portions of the body, 

 the determination is difficult, and sometimes even impossible. 

 In the present state of our knowledge, chemical reagents do 



G 2 



