COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 43 



ture rather than a substance. Moreover, there is not one pro- 

 toplasm, common to all cells, but as many protoplasms as there 

 are kinds of cells. 



There is a more or less sharp differentiation between the 

 functions of the nucleus and those of the cytoplasm. The 

 nucleus appears to be especially concerned in cell reproduction, 



FIG. i. Different types of cell composing the body. (Hadley, The Horse 

 in Health and Disease.) 



the formation of a new cell beginning with a division of the 

 nucleus of an existing cell and being followed by a division 

 of its cytoplasm. The main function of the cytoplasm, on 

 the other hand, seems to be the nutrition of the cell, and the 

 presence of at least a minimum amount of it is essential to the 

 continued existence of the nucleus. For the present purpose, 

 it is unnecessary to attempt a further discussion of those finer 

 details of the structure of the cell which have been worked out 

 by the labors of the histologist and physiologist. 



