BARBARA LEE LUND. 



by Child on Planaria. Now, considering the parallelism between 

 resistance to KCN and CO2 production and also the resistance 

 to KCN of stimulated and unstimulated worms, Child concludes 

 that the young worms have a greater metabolic rate than the 

 old ones, the starved greater than the fed ; and since my results 

 on Paramecia with respect to survival time in KCN seem to be 

 identical with these on Planaria, I was inclined to accept this 

 conclusion and apply it to these protozoa. But recent work in 

 this laboratory on the actual oxygen consumption of Paramecia 

 indicates that in the case of this animal at least KCN has no 

 effect on oxidations, even up to concentrations which kill in a 

 few hours (Lund, '18). And so we must search for the explana- 

 tion of these differences in some other direction. 



If the permeability of the plasma membrane of the protozoan, 

 like that of the surface of the sea urchin egg, changes at different 

 times in its history and with different nutritive conditions, we 

 might use that in explaining its various reactions to KCN. 

 R. S. Lillie ('16) has shown that in the case of the egg, permea- 

 bility is greatest at division and less between divisions; and, as 

 stated above, according to Lyon and others, susceptibility to 

 KCN is greatest at division and less during the time between 

 divisions. Didinia show a similar behavior, the resistance in- 

 creasing up to the fourth hour, but then decreasing again to the 

 fifth hour when 37 per cent, of them have divided. The results 

 for Paramecia, however, do not give a curve of this shape; al- 

 though the resistance increases to a marked extent in hay 

 infusion, and to a smaller extent when fed yeast, up to the very 

 time of the beginning of the formation of the constriction. My 

 data on the reactions beyond this point (that is ; the time when 

 the cell begins division) are insufficient to warrant conclusions. 

 However, my impression from the few Paramecia which did hap- 

 pen to be in the beginning stages of division while in the KCN is 

 that the resistance does not decrease previous to the time of 

 separation. 



If, on account of this parallelism with the results on the egg, 

 it is conceded that the susceptibility of Didinia is due to an 

 increase in permeability, the conclusion might be justified that 

 the high susceptibility of the starved animals is due to the same 



