576 LORANDE LOSS WOODRUFF 



sisted of a study of the effects of media contaminated with the 

 excretion products of a single form (Paramaecium) on its rate of 

 reproduction.^ The results showed that paramaecia excrete sub- 

 stances which are toxic to themselves when present in their 

 environment and reduce the division rate. This fact was inter- 

 preted as indicating that excretion products play an appreciable 

 part in determining the period of maximum numbers, rate of 

 decline, et cetera, of this animal in hay infusions. 



In view of these results it was of interest to attempt to answer 

 the following questions : 



1. Are the excretion products of paramaecia specifically toxic 

 to this species, or do they also influence the reproductive rate of 

 other species? 



2. Do other species in the observed sequence of forms of the 

 infusion fauna produce excretion products which are specific, or 

 otherwise, in their action? 



3. Do species which succeed each other in the observed sequence 

 produce substances which influence mutually their development 

 and tenure of life in the infusion microcosm? 



The present paper presents results which, it is believed, con- 

 tribute to the solution of these questions with respect to Para- 

 maecium and two hypotrichous forms, Stylonychia pustulata and 

 Pleurotricha lanceolata. . The series of experiments described 

 were made in an endeavor to determine the influence of media 

 contaminated with the excretion products of paramaecia on the 

 rate of reproduction of Paramaecium and of the hypotrichous 

 forms; and also to determine the influence of media contami- 

 nated with the excretion products of the hypotrichs on the rate 

 of reproduction of these forms and of Paramaecium, 



It was decided to study the problem with respect to paramaecia 

 and the hypotrichs because the latter have been shown, in the 

 earlier paper, to occur in maximum numbers just before the 

 dominance of the paramaecia, and because they lend themselves 

 readily to such experimental methods as the present study 

 involves. 



2 L. L. Woodruff, The effect of excretion products of Paramaecium on its rate of. 

 reproduction. Jour. Exp. Zool., vol. 10, no. 4. 



