294 L - L - WOODRUFF. 



of reproduction has never again fallen as low as it was when this 

 treatment was begun. When averaged for thirty-day periods the 

 highest rate of division appears in June and July, 1908 ; the 

 great rise in vitality which occurred in February, 1909, and is 

 shown in periods 64 and 65 of Fig. I (ten-day periods) is not so 

 conspicuous, as the average is reduced by the low rate of fission 

 during the two periods preceding. 



A similar examination of Fig. 3, in which the rate of division 

 is averaged for five-day periods, is not so instructive because the 

 influence of the rhythms is more clearly brought out during short 

 periods, so that the general trend of the curve of the life history 

 is somewhat obscured. However, when the curve is surveyed in 

 its entirety it illustrates the fact that the vitality of the organisms, 

 as indicated by the fission rate, has maintained a higher average 

 since the use of a promiscuous culture medium was instituted. 



In order to determine more fully the effect of a very constant 

 environment on this same race of Paramecium which was 

 being maintained on a varied environment, there was isolated 

 from each of the four lines, on February 19, 1909, at the I,i2ist 

 generation, a second culture, designated Paramecium I s . This 

 culture was submitted to as constant an environment as was prac- 

 ticable, according to the general method of Calkins. There were, 

 then, two cultures of the same protoplasm running simultaneously, 

 one being subjected to a varied or promiscuous culture medium, 

 and the other to a comparatively constant culture medium. As a 

 matter of precaution, and to show if there was anything 

 intrinsically deleterious in the medium provided for Culture I s , 

 its constant medium was employed at various times as a 

 temporary medium for Culture I. This, of course, simply in- 

 creased the variability of the medium of Culture I. Also, near 

 the end of the I s series, its medium was employed not only for 

 Culture I, but also for two cultures of ex-conjugant paramecia 

 (Paramecium II y and Paramecium IP) from an entirely different 

 source from that of the Paramecium of Culture I. 



The results of these experiments with a constant and varied 

 environment on the same protozoan protoplasm are shown graphi- 

 cally in Fig. 4. A glance at this curve shows that the vitality 

 of the protoplasm of Culture I s (constant environment), as meas- 



