FUNCTIONAL ACTIVITIES 



99 



the fluids of a vacuole and the color changes afford an index of 

 the degree of acidity. 



Similarly with other types of food; ferments capable of chang- 

 ing solid carbohydrates into soluble sugars have been extracted 

 from different types of protozoa, but experimenters have not 

 been equally successful in demonstrating the presence of fat emul- 

 sifying ferments. 



From all the observations and experiments it appears, then, 

 that the repair of metabolic waste involves activities of a com- 

 plicated nature, including the capture and swallowing of food 

 and the transformation of that food from the condition of solids 

 to a condition of soluble proteins and sugars. Just how even 

 these rather simple proteins, for example, amino acids, are assimi- 

 lated or added to the living protoplasmic substances is still 

 unknown, but the fact is easily demonstrated that in an incredibly 

 short time the specific protein of a Paramecium, for example, 

 becomes the equally specific but different protein of a Didinium. 

 Thus, if a single individual of Didinium is placed in a drop of 

 water with eight individuals of Paramecium, in twenty-four 



Fig. 57— PROTOZOA IN NEED OF A DOCTOR 



A, a Paramecium caudatum, which has eaten too long and too much of the same kind of food 

 and has become semi-solid; it would die if not treated. B and C, two individuals which were 

 in this condition, but were treated with dilute potassium phosphate, and are again becoming soft. 



From photomicrographs by the author 

 Magnification, 430 



