CHAPTER III. 

 THE ANIMAL CELL. 



THE cell is the unit of the manifold, variable forms of the organ- 

 ism ; it forms the simplest physiological apparatus, and as such is the 

 seat of chemical processes. It is generally admitted that all chemi- 

 cal processes of importance do not take place in the animal fluids, 

 but proceed in the cells, which may be considered as the chemical 

 laboratory of the organism. It is also principally the cells which, 

 through their greater or less activity, regulate or govern the range 

 of the chemical processes and also the intensity of the total ex- 

 change of material. 



It is natural that the chemical investigation of the animal cell 

 should in most cases coincide with the study of those tissues of 

 which it forms the chief constituent. Only in a few cases can the 

 cells be directly, by relatively simple manipulations, isolated in a 

 rather pure state from the tissues, as, for example, in the investiga- 

 tion of pus or of tissue very rich in cells. But even in these cases 

 the chemical investigation may not lead to any positive results in 

 regard to the constituents of the uninjured living cells. By the 

 process of chemical transformation new substances may be formed 

 at the death of the cell, and at the same time physiological constitu- 

 ents of the cell may be destroyed or transported into the surrounding 

 menstruum and therefore escape investigation. For this and other 

 reasons we possess only a very limited knowledge of the constituents 

 and the constitution of the cell, especially of the living one. 



While young cells of different origin in the early period of their 

 existence may show a certain similarity in regard to their form and 

 chemical constitution, they may, on further development, not only 

 take the most varied forms, but may also offer from a chemical 

 standpoint the greatest diversity. As a description of the con- 

 stituents and the constitution of the different cells occurring in the 

 animal organism is nearly equivalent to a demonstration of the 

 chemical relations of most animal tissues, and as this exposition 



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