I 



582 LORANDB LOSS WOODRUFF 



direction. It is perhaps too much to expect that experiments of 

 this nature would show conclusively such a delicate adjustment 

 as must exist between mutually associated forms in the inconceiv- 

 ably involved infusion complex. 



These experiments, however, show conclusively, it is believed, 

 that both paramaecia and hypotrichs produce substances which 

 are specifically toxic to themselves. This result is made doubly 

 secure by the very lack of concordance of the results secured from 

 the study of their reciprocal action. The data show, for example, 

 that media which have supported very heavy growths of hypo- 

 trichs are clearly inimical to the reproduction of the hypotrichida, 

 while the same media are favorable or neutral to the development 

 of Paramaecium. This rules out completely the possibility, dis- 

 cussed in the earlier paper,'* that the depressing effects observed 

 in this and the previously published experiments are the results 

 of changes in the quantity or quality of the bacterial flora (on 

 which the animals are dependent for food) in the protozoa seeded 

 and protozoa free media. 



SUMMARY 



1. Paramaecia excrete substances which are toxic to themselves 

 and these tend to inhibit the rate of reproduction. 



2. Hypotrichs excrete substances which are toxic to them- 

 selves and these tend to inhibit the rate of reproduction. 



3. These excretion products are essentially specific in their 

 action since their presence does not uniformly influence the rate 

 of reproduction of other species. 



4. The data secured, therefore, emphasize the importance of 

 specific excretion products as a factor in determining the limits 

 of development of individual forms in the infusion microcosm 

 but do not indicate that these specific products are of great im- 

 portance in relation to the rate of development of associated 

 species. 



' Vage 578. 



