PHENOMENA OF LIFE 1 9 



4. THE PHYSICAL BASIS OF LIFE: PROTOPLASM 



When the biologists of the past century turned their micro- 

 scopes upon the swarms of simpler plants and animals or exam- 

 ined the tissues of multicellular organisms, they saw the remark- 

 able substance that forms the physical basis for all the activities 

 of living organisms without realizing its importance. Felix 

 Dujardin, in 1835, first clearly distinguished this substance 

 from other viscid matter and called it " sarcode." Later inves- 

 tigators made more extended studies, but Dujardin's term was 

 not generally adopted. Sarcode was believed to be generally 

 present in the simple animals, but a different substance, called 

 protoplasm, was thought to be the living element in the complex 

 organisms. Max Schultze, in 1861, convinced the scientific 

 world that the living substance in both simple and complex 

 plants and animals is practically identical in structure, compo- 

 sition, and physiological properties. The term " protoplasm " 

 adopted at that time has persisted to the present day. 



Schultz's generalizations were of vast importance and gave a 

 great impetus to the study of fundamental problems. Huxley 

 called protoplasm the physical basis of life, a peculiarly expres- 

 sive phrase, since in protoplasm lies the ultimate explanation 

 of all vital phenomena. It is fitting, therefore, in this connection 

 to consider more fully the properties of living substance. 



Protoplasm is subject to all the physical laws of fluids. It 

 exhibits currents and flowing movements, and is influenced by 

 changes in surface tension. Its specific gravity is always a trifle 

 greater than that of water. It is usually entirely colorless or 

 gray. On account of its importance, the minute structure of 

 this living jelly has long been a favorite field for study in both 

 plants and animals. Protoplasm has been repeatedly examined 

 under the very highest powers of the microscope. Elaborate 

 methods have been devised for preserving it so that its 

 structure may be similar to that which existed during life. 

 Many theories have been advocated with regard to the finer 



