REPRODUCTION OF THE HYPOTRICHOUS INFUSORIA 71 



beef. In both of the epidemics which occurred in the cultures kept 

 on the beef medium it was very evident that the phenomenon was 

 one which affected not merely a few individuals, but that it was an 

 epidemic in the true sense of the word, and that conjugation would 

 occur in the cultures during the epidemic whenever opportunity 

 was afforded. In fact the only way by which it was possible to 

 prevent conjugation was by the daily isolation of a single individ- 

 ual such as was done in the main lines of the cultures. Inasmuch 

 as conjugation never occurred at any time in the hay culture, even 

 though in both the length of time it was kept and the number of 

 generations through which it passed it exceeded either of the cul- 

 tures kept on the beef medium, there is conclusive evidence that 

 neither the age of the organisms nor the number of the generations 

 through which they passed were potent in inducing conjugation in 

 these cultures. The determining feature was the medium used and 

 the results here recorded give definite evidence that the 'same proto- 

 plasm ' under the influence of different culture media may show fund- 

 amental differences in its life history. 



The fact that the Sbh culture kept on the hay medium did not 

 continue to live indefinitely does not show that the death of the 

 culture was due to the ending of any definite life cycle. Maupas 

 believed that 316 generations were the maximum number that S. 

 pustulata could attain. If, as in this experiment, this number can 

 be raised to 572 generations, there seems to be good reason for be- 

 lieving that, under other conditions of food and environment, the 

 number can be raised still higher and it is probable that, under 

 some conditions, they can be bred indefinitely. The work of 

 Woodruff ('lib) with Paramaecium caudatum appears to substan- 

 tiate this view. He found that this organism died out in the cul- 

 ture in which fresh medium was supplied daily but that sister cells 

 kept under other conditions continued to thrive, thus showing that 

 the death of the culture in the one case was not due to the ending 

 of any definite life-cycle, but to the fact that the environment 

 supplied was not exactly adapted to the continued existence of 

 this form. Other work by the writer, which is now in progress 

 and will be reported in a later paper, shows the same result. 



