162 RUTH L. PHILLIPS 



appears to be capable of maintaining a normal rate of metabolism 

 over an extended period. 



2. Change of food of Paramecium without change of medium. 

 This section of the work consisted of two parts. First, Para- 

 mecia which had been fed for a long time upon the bacteria C, 

 A'C, A'B'C, and M were shifted from one such food to another, 

 as, for example, animals fed upon C were washed and then 

 placed in the A'C mixture; the presumably unfavorable foods, 

 A' and B', were added to M, and other such shifts made as de- 

 scribed below. The second part of the work consisted in an entire 

 change of food. Animals which had been fed upon one of these 

 combinations were washed and placed in pure cultures of bacteria 

 used in the earlier part of the work. Table 4 gives the data for 

 the first type of food change, and in table 5 are the probable 

 errors and significance factors computed from the data of table 4. 

 The original cultures w^ere used as controls, and the change of 

 food is indicated by changing the order of the letters used, e.g., 

 cultures containing animals changed from C to a combination of 

 A' with this bacterium are designated as C A', to distinguish them 

 from A'C, the control of such a mixture. The culture, C, serves 

 as a control for all the mixtures used. 



It is evident from the data in table 4 that the change from C 

 to C'B' resulted in a serious decrease in the vitality of the animals, 

 for they could be kept alive but nine days in this mixture. 



Animals changed from C to C'A' appeared to experience an 

 increase in metabolism. This increase was too slight to be due 

 to the change in food as is suggested bj^ the significance factor, 

 1.985. The disturbing effect of the change in environment was 

 not overcome in the time during which the animals were under 

 observation. The division rate failed to reach that of A'C, and 

 it is evident that in the change from C to a food presumably 

 more satisfactory, the mere fact of the change tended to counter- 

 act the effect of the more favorable food to such an extent that 

 the animals failed to show a marked reaction to this type of 

 variation in the environment. The significance factors for all 

 the other changes save MA'B' tend to show the same thing. In 

 the case of MA'B', however, the significance factor, 3.965, in- 



