TOXIC ACTION OF KCN ON PARAMECIUM AND DIDINIUM. 22Q 



thing. If this is the case, it is obvious that there is an inconsis- 

 tency in relating permeability and rate of oxidations; for the egg 

 at division has an increase in permeability and also, if we may 

 depend upon the limited data available on this point, an increase 

 in oxidation rate, while a starved Paramecium or Didinium has, 

 according to this hypothesis, an increase in permeability and, 

 according to the facts, a decrease in rate of oxidation. The latter 

 has been found in some recent work in this laboratory, which 

 is as yet unpublished. 



It is interesting to note, in regard to the lack of resistance to 

 KCN of the starving cells, that this is in accord with the common 

 experience that tissues suffering from lack of normal blood supply 

 offer less resistance to various toxins and infections than tissues 

 which are well supplied with blood; i. e., well nourished. 



It is evident that the experiments given above on Paramecium 

 and Didinium, and the results on eggs of echinoderms by others, 

 and those on lower invertebrates, offer a promising avenue of 

 approach to an understanding of what some of the fundamental 

 conditions in the cell are which determine the degree of resistance 

 of cells to toxic substances. 



SUMMARY. 



1. An attempt was made to discover what factor or factors 

 are responsible for the observed differences among individuals of 

 a pure line of Paramecia and Didinia living in the same culture 

 medium ; e. g.. hay infusion. What are the differences in a proto- 

 zoan cell which cause difference in response to apparently iden- 

 tical external conditions at different times? 



2. Survival time (resistance) of Paramecia and Didinia in 

 solutions of KCN was selected and used as an index because of 

 the generally supposed relation of the toxic action of KCN to 

 the rate of oxidation in cells. 



3. All the data on survival time of Paramecium and Didinium 

 were obtained by observations on individual cells and not by 

 estimating the average survival time of large numbers of cells as 

 is usual in such experiments. In this way the variation in resis- 

 tance of the cell at different times during the period between cell 

 divisions was followed accurately and is summarized in curves. 



