PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 477 



permanent cultures given above (p. 474), in which it is shown that 

 four lines out of eight of quadrant A died out entirely whereas 

 three lines (two of these due to a pathological division which may 

 be considered an indication of weakness) died from quadrant B, 

 and one each from quadrants C and D. In order to test the 

 relative vitality' more directly, however, the division rate o! rep- 

 resentative specimens from each line was carefully kept for thirty 

 days in October and November, and again for forty-two days in 

 February and March, The rates were averaged for five-day peri- 

 ods, the results of both tests being shown in the accompanying 

 graphs. These are based upon the averages for five-day periods 

 of all the lines of each quadrant. 



The division rate is generally accepted as an index of vitality 

 since it represents the rapidity with which the organisms reach 

 the limit of growth or the rapidity of metabolism. It is evident 

 from this test, together with the evidence from the permanent 

 cultures, that the pure lines derived from quadrant A were physi- 

 ologically weaker than those from the other quadrants for a period 

 of at least five months, a result shown in the first test by the av- 

 erages of the division rates of all lines of each quadrant — 0.65 for 

 quadrant A, 0.908 for quadrant B, 0.81 for quadrant C, and 0.95 

 for quadrant D. Or, in one hundred days a typical representa- 

 tive of A would have divided 65 times, of B, 90 times, of C, 81 

 times and of D, 95 times. 



^ The March vitality test (diagram 1) is interesting as showing 

 a much closer agreement amongst the pure lines from different 

 quadrants. For this test we are indebted to Mrs. Binkley who 

 carried it on for more than six weeks under our direction and with 

 our methods. Her results, worked out biometrically, will be 

 published independently. It must be noted that a period of 

 four months intervened between the first and second tests all 

 lines in this interval being maintained as nearly as possible under 

 identical conditions, the cultures being replenished at the same 

 times and with the same media. The graphs show that the four 

 lines of quadrant A are now almost if not quite as vigorous as 

 those of the other quadrants, all lines indicating greater vigor 

 than at the period of the first test. 



