ADAPTATION' OF PARAM.^ECIA TO ENVIRONMENTS. 6 1 



served as a control and for comparison with the P. caudal um 

 culture, there are no results to be recorded which are not in 

 (in in- agreement with these already published. The culture has 

 kept on the even tenure of its way and is now, after over four and 

 "in- half years of daily observation, at tin- 2.7051!! generation, 

 and in every way in as normal morphological and physiological 

 londition as at the start. Given a favorable environment, thi- 

 race dearly has unlimited power of reproduction without con- 



iin or artificial stimulation. 



I In | .1 d^rec culture of Paramccc ium caudatiin: \ which \\a- 

 -ubi' - led 1 1 "in the start to the 500 th generations (twelve and one 

 halt montli-i to identically the same treatment and culture me- 

 dium a- i he I y . aitrclia culture, showed during the lir-t 350 genera 

 lion- K'ln months) essentially the same rate of repri.diieti.m 



die <!ur<-!i(i culture. However, an examin.iiioii <>l the daia 



I i and 2) shows that a slow decline in division rai. 



in ai the -iart which finally resulted in a race of cell- PD--I- ini; 

 man\ "t i lie morphological and physiological characteri-tii - de- 

 scribed \<\ ('alkins 1 in liis careful study o!" pure line- of ihi- 

 species "i Paramacium. Alter about tin- 4501)1 ^eneiaiinn it 

 became iin leasingly ditVicult to keep the animal- ali\e mi the 

 slide- iii the culture medium which was supplied fiv-h daily. 

 llo\\e\er. the cells left over from the daily isolations, which were 

 alli'ued I" acru mil late in the old culture liquid, appeared healthv 

 and ii'iit'imed to reproduce slowly. It the-e \\eiv transferred 



n in lre-h medium they would di\'ide a few tinii-- and then 

 <lie l-'inallv lhe\- would not live twenty-four hour- in the I'n -li 

 medium. 



l'\ -ub-tiiuting from the "stock" in thi- \\a\\ the direct line- 

 "I ihe culture were kept replenished for nearK tlirc'e month-; bin 

 ImalK it uas evident that it was impo ible i" cmitinne the 

 culture b\ ilii- method, so that the exact number "t ^< in-iation- 

 could In- determined, and according . at the -,o"ih generation, 

 the method uas abandoned, and the animal- \\eiv thereafter 

 aiiicd iii -mall tlasks of old infusions. /. e., lhe\ were bred in a 

 i "inparati\ cl\ large volume of the same type of medium to \\ hich 



1 (",. X. (\ilkin-: " Ilir I ilr Cycle of l'<ii.. .:i<ltltnm." \r,lr 



En nismcn. Bd. 15, i, 190.'. "Death of th V Series ol 



t onclusions." Jum. l-.\pfr. '/.. Vol. i, no. .;. 



