26 



PRINCIPLES OF ANIMAL BIOLOGY 



haps intended to convey the idea of insignificance. Dujardin (Fig. 

 15), a French naturahst, appears to have thought it worthy of more 

 attention, and described it in 1835 under the name "sarcode" (soft 

 substance). He tested its sohibihty, and its behavior with certain re- 

 agents, such as alcohol and the acids, thereby satisfying himself that it 

 differed from other jelly-like substances (gelatin, albumen, etc.) with 

 which it might be confused. But either because Dujardin had studied 

 the sarcode only in worms and Protozoa and a few other low forms of 

 animal life, or because his diffidence forbade his making any larger claim 

 for it, this substance was supposed to be found only in the lower animals. 

 The general occurrence of this substance, however, could not long avoid 

 discovery. Hugo von Mohl, in 1846, observed the living part of plant cells, 



Fig. 16. — Max Schultze, 1825-1874. {^From Garrison's History of Medicine.) 



distinguishing it from the walls and vacuoles, and called it protoplasm. 

 This name, used earlier by Purkinje, von Mohl succeeded in bringing into 

 common use. Gradually it dawned upon biologists that this matter is 

 found in all living things, that it is in fundamental respects alike in all 

 of them, and that this, rather than the walls, is the important feature of 

 cells. In the absence of cell walls, this protoplasm is the cell. Of a 

 number of investigators who contributed to this fortunate issue of the 

 problem of the cell, mention should be made of Max Schultze (Fig. 16) 

 who, probably more than any other one person, brought conviction of 

 the truth of the idea just stated to the minds of all biologists. 



Additions. — The bare statement that all living things are composed 

 of cells is also inadequate in at least one structural respect. It was 



