196 GARY N. CALKINS. 



they would become abnormally active and would finally die. 

 The division-rate gradually increased during the month of August 

 until, in the last ten days, they averaged six generations. Finally, 

 in September, the attempts to get them back on the old diet of 

 hay-infusion were successful, and then the division-rate went up 

 at once to twelve times in ten days, and a month later, they were 

 dividing at the rate of fifty times a month. 



This experience showed that " rejuvenescence" in the Maupas 

 sense, can be brought about without the aid of conjugation. Had 

 it not been for the extract of beef, or some other equally beneficial 

 substance, all of the organisms would have died, and, like Mau- 

 pas, 1 Joukowsky 2 and Simpson, 3 I should have assumed that 

 their possibilities of continued living had been exhausted and that 

 they had died from "old age" in the igSth generation. 



From November ist to December loth the curve shows that 

 the division-rate and the general vitality gradually decreased, and 

 by the middle of December, a similar experience to that of mid- 

 summer threatened the cultures. Profiting by that -experience I 

 took the precaution of giving some of the individuals beef-extract 

 before they got too weak, while others were continued on the 

 hay-infusion. All of the latter died within a few days. Those 

 that had been fed with beef-extract for 48 hours continued to 

 live when put back in the hay-infusion, and they continued 

 through another cycle of almost three months without treatment 

 again with the beef. 



From the middle of December on, the cultures were continued 

 under slightly different treatment. Two of the four lines of As 

 (A-i and A-2) and two of the four lines of Bs (B-i and B-2), 

 were treated once per week for 24 hours with beef extract. This 

 treatment was continued until the middle of March, when they were 

 given hay-infusion without further variation. The other lines 

 of As and Bs, viz., A- 3, A-4, and 6-3, and 6-4, were treated 

 in December with the beef-extract and then kept on hay-infusion 

 without further change. By this treatment it was possible to 

 compare the general vitality under conditions of a more or less 



i Maupas, E., Archives d. Zoo!, exper. e. gen. (2), VI. and VII., 1888, 1889. 

 sjoukowsky, D., Verh. nat. Med. Ver. Heidelberg, 1898, Bd. XXVI. 

 3 Simpson, J. V., Proc. Roy. Soc. Edinburgh, 1901. 



