82 



PHYSIOLOGICAL ACTIVITIES OF THE PROTOZOA 



division stops, and the animal, unless treated, invariably dies. The 

 trouble seems to be due to the lack of oxidative processes, possibly 

 because the nucleus fails to provide the necessary ferments. The 

 tension is relieved and activity again started up by treating such an 

 organism with salts like potassium chloride or potassium phosphate, 

 or with the more complicated salts contained in an extract of pancreas. 

 It is possible that in the latter case the extracts from the pancreas have 

 some direct effect upon the granules in question, but such an explana- 

 tion cannot account for the successful results with the simple potassium 

 salts, and it seems more probable that the explanation lies in the fact that 

 the stimulants act directly upon the nucleus and cause it to resume 

 a neglected function. This conclusion is borne out by the fact that 

 the tension is first relieved in the immediate vicinity of the nucleus 

 (Fig. 26), and then progressively toward the ends of the organism. 



FIG. 26 



Paramecium aurelia in condition of protoplasmic "stability" (extreme left) and resumption 

 of normal "labile" condition as a result of treatment with salts. 



The inner processes of digestion are entirely unknown in the sapro- 

 phytic forms of protozoa and in the parasitic forms, but there is reason 

 to believe that it is taken up at the point of granule formation in other, 

 holozoic, forms. In parasites like trypanosoma living in blood 

 lymph the nourishment is probably derived from the digested food 

 materials carried by the blood and upon which the organisms, pre- 

 sumably, live as saprophytes. Such forms are quite different, physio- 

 logically, from intracellular or intracorpuscular parasites, such as 

 coccidia, malaria organisms, etc., which live upon the substance of 

 the cells or blood corpuscles. 



