2Q2 L. L. WOODRUFF. 



III. DESCRIPTION OF CULTURES. 



Culture I has attained, during the first twenty-six months of 

 its life, the 1,23 8th generation. The average rate of reproduc- 

 tion for the entire period has been over one and a half divisions 

 per day, and during not a single ten-day period has the average 

 rate fallen as low as one division in two days, while during several 

 ten-day periods the rate has averaged over two and a half 

 divisions per day. 



Fig. i shows, by the familiar block method, the average rate 

 of division of Culture I for ten-day periods. Especial emphasis 

 is put on the character of this curve as the results of Calkins' 

 cultures are plotted for ten-day periods. A study of this diagram 

 shows that the life history falls naturally into two parts. The 

 first extends from period one to period thirty, and the second 

 extends from period thirty to the present time. These two 

 major parts of the curve are coextensive with different methods 

 in the treatment of the culture. The culture medium used dur- 

 ing the periods covered by part one was very much more uniform 

 than that used during part two ; the decidedly varied environ- 

 ment not being employed until February, 1908. The effect of 

 this treatment is shown in the decided change in the character 

 of the curve of the division rate from that period to the present. 

 The general vitality of the protoplasm is considerably higher as 

 is shown by the fact that only once since that time has the curve 

 for a ten-day period fallen below one division per day, and that 

 period represents the culmination of the more or less severe 

 treatment which the culture received when it was carried to Balti- 

 more during convocation week. However, to the change of 

 water and other conditions incident to the journey is apparently 

 to be attributed the stimulus which enabled the culture to attain 

 a short time after an average rate of nearly two and three quarters 

 divisions per day (see Fig. I, periods 64 and 65), the highest 

 reproductive power shown in the life history for any ten-day 

 period. 



A study of Fig. 2, which is plotted by the same method as 

 Fig. i except that the periods are of thirty-day instead of ten- 

 day duration, also shows clearly the effect of the varied culture 

 medium which has been in use from February, 1908. The rate 



