EFFECT OF EXCRETION PRODUCTS OF INFUSORIA 



581 



'plus') the average division rate was above that of the controls 

 and beyond the hiTiits of error as indicated by the difference 

 between the two controls. 



It is apparent from this table that the four experiments which 

 repeat the work already published on Paramaecium substantiate 

 completely the conclusions there reached that paramaecia excrete 

 substances which are toxic to themselves when present in their 

 environment and inhibit their rate of reproduction. It is also 

 evident that the hj^potrichs excrete substances which inhibit their 

 rate of reproduction since the division rate was reduced in seven 

 out of the eight experiments — the exception indicating neutraUtj''. 



The results from the reciprocal action of the P and the H media 

 are not so conclusive. Taken at their face value the figures would 

 indicate that paramaecia excretion products are, on the whole, 

 neutral or slightly inimical to the hypotrichous forms, while the 

 latter's excretion products are, on the whole, slightly favorable 

 to paramaecia. 



Accepting for the moment this interpretation of the results, the 

 data are, a priori, decidedly interesting. It having been shown 

 in an earlier paper that, on the average, the hypotrich maximum 

 at the surface of an infusion is passed before the corresponding 

 period in the development of the paramaecia is attained, one 

 would expect, if the hypotrichous species and the paramaecia 

 mutually influence each others life in the infusion microcosm that 

 the hypotrichs' products would produce a favorable medium for 

 the approaching paramaecium maximum, while the products of 

 the increasing hordes of paramaecia would render the medium 

 unfavorable for the hypotrichs and so contribute to their decline. 

 Obviously, however, the data secured are not sufficiently concor- 

 dant to render this hypothesis secure though they trend in that 



