52 THE LIVING WORLD. 



We have, it is true, taken one step farther toward 

 simplifying the life problem when we step from 

 the study of the cell to the study of protoplasm, but 

 we have not reduced life to a common factor. There 

 is, indeed, no such thing in nature as protoplasm in 

 general, but only particular kinds of protoplasm. 

 Protoplasm can produce new protoplasm, but not 

 new protoplasm in general, only new protoplasm just 

 like itself. The amoeba can make new amoeba pro- 

 toplasm and no other, while the nerve cell is capable 

 of giving rise to new nerve protoplasm. The study 

 of the variations among protoplasm has progressed 

 until we are slowly ceasing to look upon it as a 

 definite substance. The microscope investigation of 

 recent years has shown that not only is it chemically 

 complex, but it can no longer be regarded as physi- 

 cally homogeneous. Several distinct chemical com- 

 pounds have been discovered in it. Within the 

 simplest protoplasm has been found an extremely 

 complex structure. There is a dense reticulum 

 made up perhaps of hollow threads, containing 

 minute granules and a liquid matter (Fig. i). The 

 granules are united in various ways to form groups. 

 To-day we may almost say that the study of the 

 structure of protoplasm promises to become as com- 

 plex a subject for the future as the study of the 

 animal kingdom on a large scale has proved to be in 

 the past. Instead of looking upon protoplasm as 

 the primitive life substance, at the present time, 

 most special students of protoplasm would regard 

 the granules as more likely the fundamental part and 

 all else derived. These granules are excessively 



