250 EVOLUTION AND ANIMAL LIFE 



ground substance, we do not believe at all that this struc- 

 tural differentiation is the ultimate physical make-up of the 

 mysterious substance protoplasm. We readily believe there 

 may exist an ultramicroscopic structure of great complexity. 



Buffon suggested that the living stuff is composed ultimately 

 of tiny structural units, which he called organic molecules', 

 these molecules are universal and indestructible; they do not 

 increase in number or decrease; when united in groups they 

 form organisms; when an organism dies its organic molecules 

 are freed but not destroyed, and later may help compose other 

 organisms. Bechamp believed in similar living micromeric 

 units called microzymes, created directly by the Supreme Being, 

 indestructible and strewed everywhere in earth, air, and water. 



Herbert Spencer postulated the existence of so-called phys- 

 iological units: living units all of the same structure, active 

 because of their polarity of form and of molecular vibrations, 

 in size and character midway between molecules and cells, 

 small but complex and possessed of a delicate and precise 

 polarity analogous to that of the molecules of crystalline sub- 

 stances, a polarity which gives them the capacity to group 

 themselves into organic parts and wholes. Other theories 

 similar to Spencer's assume a special physicochemical en- 

 dowment of the chemical molecules in the organic body (Ber- 

 thold), or a special electrical endowment of the life units (Fol), 

 or a special chemical one (Altmann and Maggi), or, finally, a 

 special vital one (Wiesner). 



Darwin proposed a theory to explain how the germ plasm 

 could unfold into the whole body, called the theory of the 

 pangenesis of gemmules. Darwin postulated the existence in 

 the body of a host of life units called gemmules to be found 

 in all the various body cells, capable of rapid self-multiplica- 

 tion and of a migratory movement through the body, the direc- 

 tion and goal of which movement is determined by delicate 

 affinities existing among the various gemmules. When a gem- 

 mule enters an undifferentiated or developing cell, as yet 

 gemmuleless, it controls the development of that cell. Thanks 

 to the delicate and precise affinities of the gemmules, they 

 always get to just where they should, to produce harmonious 

 development; but in the germ cells lodge gemmules from all 

 over the body, so the development of these cells results in a 

 new whole body. 



