1 68 ANIMAL AGGREGATIONS 



talysis in yeast. Apparently he used very careful technique, washing 

 his transplants and plotting a growth curve based on a number of 

 examinations at different phases of the culture. He finds that in 46 

 cultures with synthetic media whose volumes ranged from 2 to 

 146 cu. mm. he cannot attribute any differences observed to changes 

 in volumes, as would be required if Robertson's hypothesis of allelo- 

 catalysis holds for yeast. With 57 cultures, containing bios and vary- 

 ing from 0.5 to 362 cu. mm., he observed a tendency for more rapid 

 growth in the cultures with the larger volumes. In only 2 cases out 

 of 8 near the minimal volume did he find evidence of acceleration in 

 the cultures. The statistics on mortality of the cultures show that 

 those started with 2 cells usually have a higher viability but that 

 the percentage of difference is not great. He concludes that allelo- 

 catalysis does not occur in the yeast studied. 



Cutler and Crump (1925) also repeated their experiments with 

 Colpidium, thoroughly washing their animals before transfer. They 

 again failed to obtain evidence of the stimulation demanded by 

 Robertson's hypothesis. It may be that their technique differs suffi- 

 ciently from that of Robertson to account for some difference in 

 results, since the infusorians which Robertson washed were fre- 

 quently injured in the process while Cutler and Crump found no 

 deleterious effect from their washings. 



Calkins (1926) gives the results of 60-day experiments with 

 Uroleptus, in which i, 2, 3, and 4 animals were introduced into i 

 drop of fresh medium, respectively. The division rate was found to 

 be inversely proportional to the initial number of individuals inocu- 

 lated. 



Returning to this problem in 1927, Robertson states that all of 

 the data and conclusions concerning allelocatalysis in Infusoria 

 which have been issued from his laboratory in recent years remain 

 valid, save that they may apply to the associated food organism and 

 not to the Infusoria themselves. 



Robertson, in further considering the possible reasons for the 

 discrepancy between his own work and that of his critics, stresses the 

 need of being sure that the animals isolated to test for allelocatalysis 

 should have the same division rate and that this effect is shown 



