ZOOLOGY: G. N. CALKINS 
99 
The F series was started with an ex-conjugant of the C series in the 86th 
generation, and died December 21 in the 317th generation, ten days earher 
than the parent series. The I series was taken from the F series in the 143d 
generation and is still living actively in the 305th generation. The L series 
came from this I series in the 199th generation and is actively dividing in the 
118th generation. An N series (not included in the table) has recently been 
started from the J series in the 188th generation. 
While table 1 by itself, shows clearly enough that conjugation restores 
vitality to an optimum, the results may be shown still more strikingly by a 
comparison of longer periods of time whereby minor fluctuations are less 
conspicuous. I find from the records of the conjugation tests of all series, 
that conjugation does not begin to take place until from fifty to seventy days 
from the start of a series. I have chosen the period of the first sixty days, 
therefore, as representing the period of sexual immaturity. The records 
show, furthermore, that this is also the period of optimum metabolic activity. 
Comparing the mean division rate of a filial series in this first sixty day 
period, with the division rate of the parent series for the same calendar sixty 
days, shows the extent, in division activity, to which conjugation has re- 
stored vitality to the parent protoplasm. Thus, during the first sixty days 
of the C series, the five lines had a mean daily division rate of 8.6333, or each 
individual averaged 1.726 divisions per day, or in ten days, 17.2666 divi- 
sions. In the same sixty days, the parent A series, starting at the 78th gen- 
eration, had a mean division rate of 7.8666 daily, each individual averaging 
15.7333 divisions in ten days. The difference, 1.53, indicates the average 
increase, in number of divisions in a ten-day period, of each individual of the 
C series, over each individual of the parent A series. In this case the filial 
generation was taken from the parent when vitality of the latter was near its 
optimum, and a small discrepancy between parent and offspring is to be ex- 
pected. With increasing age of the parent, and with corresponding reduc- 
tion in vitality of its protoplasm, one might reasonably expect that conju- 
gation between two such weakened individuals, would result in a filial gen- 
eration in which the discrepancy between parent and offspring would remain 
practically the same as above. The results, however, do not support this 
expectation; on the contrary, the discrepancy increases with age of the parent 
protoplasm, as shown in table 2. 
It is evident, from the foregoing, that conjugation results in the complete 
restoration of vitality regardless of the age or the weakened condition of the 
parent protoplasm, although both parental and filial series are fed at the same 
times on exactly the same culture medium. This is particularly striking in 
the case of the J series. 
Table 2 also shows that all filial series return to a certain optimum of 
metabolic vigor as a result of conjugation, a vigor represented by from 17.1 
to 17.9 divisions per individual in ten days. From this optimum there is a 
gradual loss of vitality which is common to all series and which finally leads 
to death from old age. This is clearly shown in table 3. 
