4 GENERAL CONSIDERATIONS 



organization having the possibihty, or the potential of vitality. Such 

 activity of protoplasm involves the interaction of its component parts 

 with one another and with the environment. Life thus may be conceived 

 as static, or analogous to an automobile in its garage, and dynamic, as an 

 automobile in motion. A dried rotifer is almost, if not entirely static, 

 but retains its organization; place it in water and it becomes dynamic 

 within a few minutes. Similarly with an encysted protozoon, which, 

 within its cyst walls is not freely exposed to water and oxygen but 

 retains its specific organization and is apparently static and, like a dried 

 rotifer, it may remain in this desiccated condition for years without losing 

 its potential of vitality so that, when again placed in water, or culture 

 medium, it soon emerges from its cyst, develops motile organs and other 

 adult structures, and begins again its metabolic activities. The protoplasm 

 within the cyst is undifferentiated, but soon after active metabolism 

 begins, it becomes differentiated with structures peculiar to the species. 

 After this the organization changes with each act of a metabolic nature. 



Fundamental and Derived Organization 



We have reason, therefore, to speak of a fundamental organization of 

 protoplasm, characterized by undifferentiated protoplasm of a cyst, or 

 of an Qgg, and of a derived organization which comes from the funda- 

 mental through metabolic activity and is characteristic of the adult and 

 all of its parts. It follows that death is not of necessity the absence of 

 vitality but is due to the derangement or breakdown of the organiza- 

 tion. 



Thus all species of Protozoa have within themselves the potential 

 of an endless existence, subject, of course, to the vicissitudes of the 

 daily life of the adults, each of which is the custodian of a limited portion 

 of the fundamental organization. 



Some Ecological Considerations 



As well known. Protozoa may be found wherever there is moisture 

 without deleterious substances and the same species may be found in the 

 littoral waters of the sea and in inland fresh-water lakes, ponds, and 

 pools. Although many species are cosmopolitan, they tend to accumulate 

 in certain places where the environments best suit their needs; hence it 

 is possible to outline certain ecological limitations, although these must 



