158 RUTH L. PHILLIPS 



it could be seen that there was in reaUty. a steady dechne in 

 the power of the chance mixture M to maintain a normal rate of 

 metabolism in Paramecium, and that the seemingly abrupt 

 failure of this mixture was, after all, only apparent. 



The streptothrix C, the only organism of those tested which 

 proved to be a satisfactory food when used in pure culture, is a 

 filamentous organism, the individual filaments of which are too 

 large for Paramecium to ingest. The animal w^as, therefore, 

 forced to subsist upon the fruiting bodies or upon very young 

 filaments. The questions might be raised: Was not the low 

 metabolic rate of the animals fed with this organism due to an 

 insufficient amount of food? Was the supply of fruiting bodies 

 adequate? It is probable that the food w^as quite adequate in 

 amount and the increases in activity noted for these animals 

 were not due to any increase in the reproductive power of the 

 streptothrix. It is far more likely, since they occurred synchro- 

 nously with similar increases in other cultures, that they were 

 associated with rhythms and had no direct relation to food. 



The mean division rate for C for the entire series of observa- 

 tions was 1.033. An inspection of table 3, shows that the divi- 

 sion rate fell below this mean three times; at the beginning of 

 the experiments and during the second and fourth periods. 

 During the other periods it was slightly in excess of the mean 

 rate. On the whole, it showed less variation from the mean 

 than the other two artificial mixtures. The fourth period, dur- 

 ing which the rate dropped below the mean, was marked by a 

 fall in metabolic rate in all cultures. It is possible that the 

 greater range in temperature combined with an unsatisfactory 

 condition of M was suflfi.cient to cause the death of the animals in 

 this mixture. 



When A'C is compared with C, it is evident that the addition 

 of A' to C caused a marked acceleration or stimulation of the 

 metabolic rate of Paramecium. The division rate exceded that 

 of C during all the periods. The percentages of high divisions, 

 low divisions, and deaths show an increased metabolism. There 

 was more fluctuation in the death rate for A'C, and it was greater 

 than for C during the third period. It was found in computing 



