ORGANIZATION AND VITALITY 



113 



outlined the individuals are isolated after each division, a treat- 

 ment which, for some reason which no one has explained, pre- 

 vents encystment or conjugation and the reorganization which 



12 3 4 5 6 7 8 9 10 U 12 13141516 17 1819 20 21 22 23 24 25 26 27 28 2U 30 31 32 3334 3536 37 38 3940 41 

 Fig. 64— A VITALITY CURVE OF UROLEPTUS MOBILIS 



The spaces numbered 1, 2, 3, etc., represent successive 10-day periods; the horizontal rules 



represent the average number of divisions in ten-day periods. Thus in the first ten-day period 



the race divided IS. 3 times; in the 20th period they divided only six times. The dotted-line 



curve is the history of a single race, while the solid curve is an average of many races 



From a graph made by the author 



follows those processes. At any time after the first sixty days, 

 if reserve individuals, all of which are closely related to the 

 isolated individuals, are put together in a culture dish, they will 

 conjugate. Reorganization is effected and the ex-conjugant starts 

 a new cycle with the optimum division rate. Thus at the point 

 marked X on the graph, when the parent protoplasm was divid- 

 ing at the rate of six divisions in ten days, one of the ex-conju- 

 gants starting a new cycle was dividing at the rate of sixteen 

 divisions in ten days, and under exactly the same environmental 

 conditions. For a period of ten years and by similar procedures 

 one hundred and thirty-five cycles of ex-conjugants were followed 

 through to the death of the cells, each cycle running out in ap- 

 proximately one year. Vitality of that particular bit of proto- 

 plasm, isolated in 1917, was maintained at the constant level by 

 periodic reorganizations by conjugation as long as the experiment 

 continued. 



