136 PROTOPLASM 



molecule which is presumed to be an isoprene, linear in form and 

 spirally wound (a helical coil). That this is true seems likely 

 from the successful attempts (by W. H. Carothers of the du Pont 

 Laboratories) to produce artificial rubber. Synthetic rubber is 

 an emulsified isoprene (u-polychloroprene) which is not stabilized 

 with protein membranes; the elastic qualities cannot therefore 

 reside in the latter. 



The Protoplasmic Emulsion. — Among natural emulsions, that 

 which is of most interest to us is the protoplasmic one. The 

 behavior and significance of the living emulsion we shall have 

 occasion to refer to very often. In its coarser, microscopically 

 visible structure, protoplasm is an emulsion of fat, yolk, and 

 other globules dispersed in a complex aqueous medium; but this 

 structure is a superficial one and not of fundamental significance. 

 Those who regard protoplasm as a fine emulsion in its ultramicro- 

 scopic structure have developed some interesting theories based 

 on this assumption. These will be taken up under the vital 

 processes that they are said to explain. 



