CHAPTER I 



GENERAL CONSIDERATIONS 



Gary N. Calkins 



Although Protozoa are known in all parts of the world, and evidence 

 is at hand that they — in some cases even the same genera — have lived and 

 thrived in all periods of the earth's history, little has been accomplished 

 to show how this remarkable phenomenon of longevity has been brought 

 about. Within the last century, however, the matter has been the subject 

 of many studies, both theoretical and experimental, although the latter, 

 it must be confessed, are nearly always combined with the former. 



Life and Vitality 



For many years it has seemed to the present writer that life and 

 vitality are concepts which have so often been confused that at the pres- 

 ent time they are held by many biologists, and by most philosophers, to 

 be synonymous. There is reason, however, especially in connection with 

 the protoplasm of Protozoa, for distinguishing between them, as I have 

 maintained in my recent textbook. The Biology of the Protozoa. 



It is generally recognized that life cannot be measured nor analyzed 

 as such, except through its manifestations of vitality. It has long been 

 known that each type of living thing has a specific organization which 

 is carried on, subject to adaptations through reactions to the environment, 

 or by inheritance, from generation to generation. At the present time we 

 do not know what this finer organization is, but it is assumed that specific 

 proteins form the basis of species differences, and that these, in combina- 

 tion with water, carbohydrates, fats, and salts of different kinds, pro- 

 vide the materials for metabolic activities. Thus we have the possibility 

 of arriving at at least two concepts; first, the concept of the physical 

 and chemical make-up, or, in general, the organization; and second, the 

 concept of that same organization in action. I would apply this second 

 concept to protoplasm during its activity and would limit the term 

 vitality to this activity. It follows that life may be defined as specific 



