CHAPTER IV. 

 GENERAL PHYSIOLOGY. 



LIFE, ORGANIZATION, AND VITAUTY. 



There is no doubt that our knowledge of the structures of 

 Protozoa far outstrips our knowledge of their functions. The 

 minute size of the individuals and the inadequacy of microchemical 

 tests make it extremely difficult to follow out any physiological 

 process to its end, and masses of single cells in pure culture are 

 impossible to obtain, although an approach in this direction is 

 made by the so-called "pure-mixed" cultures of Bacteria and 

 Protozoa. 



It must not be overlooked that j)hysi()l()gical problems here for 

 the most part begin where similar ])roblems of the INIetazoa leave 

 oft", namely in the ultimate processes of the single cell. Here the 

 functional activities have to flo with the action and interaction of 

 different substances which enter into the make-up of protoplasm 

 and, at the jjresent time, are beyonfl our powers of analysis. A few 

 of these activities may be duplicated individually and apart from 

 correlated functions, in the laboratory. Or specific reactions between 

 specific chemical substances may be obtained as, for example, the 

 digestion of fibrin by fluids extracted from the protozoon proto- 

 plasm; or in a physical sense the reversal of the sol and gel states 

 in colloidal mixtures. Such individualized processes, however, give 

 little idea of the infinite play of forces continually operating in 

 living protoplasm all of which, harmoniously working together, 

 make up the phenomena of \'itality and distinguish living from life- 

 less matter. 



Protoplasm is an aggregate of chemical substances in colloidal 

 form and in the physical state of a complex emulsion. Groups of 

 chemical substances known as nucleins, nucleo-proteins, albumins, 

 carbohydrates, lipoids, salts and water are universally present and 

 the various vital activities consist of actions, reactions, and inter- 

 actions between and amongst these different substances. Aggre- 

 gates of substances become local centers of special activity; these, 

 the })lastids of the cell enumerated in Chapter II, frequently have a 

 definite form and size and can be demonstrated m()ri)h()l<)gically. 

 Such })lasti(ls do not lose their labiHty or functional activity with 

 the processes in which they participate. Other substances, however, 

 are chemically and physically changed by the processes through 



