64 LORANDE LOSS WOODRUFF. 



present generations. The only way to prove that conjugation 

 has not occurred is to make the conditions such that it is an im- 

 possibility for it to occur, ;'. c., by daily Isolations un<l record of 

 generations. Since the physiological condition of this pedigree 

 culture prohibited this after the 5OOth generation. 1 have adopted 

 the method employed by many investigators of problems of this 

 nature and allowed the Infusoria to accumulate in considerable 

 numbers. I have, however, in order to increase the accuracy of 

 the method, confined the cells in as small a volume of old infusion 

 as possible and have examined the flasks at frequent intervals 

 for signs of conjugation. 1 have never seen a single pair of con- 

 jugants in all the multitude of cells which I have examined, and 

 it seems highly improbable that conjugation has occurred. It 

 should be emphasized that, if conjugation has taken place, it has 

 not so altered the physiological condition of the cells that they 

 will live under the slide method of culture. 



This culture, then, is apparently in as healthy a condition as at 

 the beginning of the work, but it has become so modified that 

 the animals are unable to exist in small volumes of fresh infusions. 

 This is a decidedly interesting result in the light of the work of 

 other investigators on Param&cium caudatum, since it shows that 

 a race of cells may exhibit all the signs of "senile degeneration" 

 at the end of a typical "cycle" of generations, and still may 

 appear healthy and exhibit a normal rate of reproduction when 

 put under other conditions which approximate what is probably 

 the usual environment of wild parama>cia. 



In other words, this culture of P. caudatum substantiates the 

 conclusion of Calkins that, under the conditions of his experi- 

 ments, this organism may pass through a "cycle" which finally 

 terminates in death; but it further shows that this "cycle" is 

 probably an artificial one which is brought about by the sub- 

 jection of the race to an environment which is not suitable for 

 its prolonged existence. This culture also shows that pure lines 

 of different species of ParamdBcium (aiirclia and caudatum} are 

 adapted to different environmental conditions, in virw ol the tact 

 that the- race of 1* . aitrclia has thrived indefinitely on the same 

 culture medium which has proved increasingly unfavorable for 

 the race of P. caudatnm. It may be that I his is actually a specific 



