404 Pedigreed Race of Paramcücium [Mar. 



observed (in this case cell divisions) at the temperatures Tj and 

 Tq respectively, stated in degrees Celsius, it is found that the tem- 

 perature coefficient derived from the above experiment is 2.74. 

 Again, if the coefficient is computed for the rate of division of, for 

 example, lines i, 2, 3, and 4 (of the eight lines) at 28°, and of 

 lines I, 2, 3, and 4 (of the eight lines) at 24.5°, it is found to be 

 2.71. Likewise Qio for only line i is 3.04. Obviously these 

 coefficients are in remarkable agreement with the demands of van't 

 Hoff's law. 



In the experiments described, a comparatively limited number 

 of lines of cells were tested for a considerable period of time at 

 temperatures within the optimum zone of the organisms. It 

 seemed advisable also to determine the effects of different tempera- 

 tures on a large number of lines of cells for a shorter period of time. 

 This not only afforded, in a sense, a reciprocal experiment, but also 

 allowed the organisms to be tested at temperatures 7° apart instead 

 of only 3.5° apart, because for a short period, as five days, a normal 

 rate of division could be obtained at 21°. Accordingly 100 lines 

 of cells were subjected to 28° C. for five days and a similar num- 

 ber to 21° C. for five days. The 100 lines at 28° gave a total of 

 662 divisions, while the 100 lines at 21° gave a total of 336 divi- 

 sions. Computation of Qjo from these data by the formula pre- 

 viously employed gives 2.63, which again is clearly in remarkable 

 agreement with van't Hoff's rule. 



In Order to test the coefficient at a lower ränge of temperature, 

 three series of eight lines of cells each were carried for five days 

 at 28°, 24.5° and 16° C. respectively. It was necessary to make the 

 period short because the organisms were not long able to endure 

 16°, and beyond five days the rate of division was obviously abnor- 

 mal because the cells showed a high mortality. The records of this 

 experiment show that 71 divisions occurred in the eight lines at 28° 

 for five days, 44 divisions at 24.5°, and 18 divisions at 16°. öio 

 for the division rates at 28° and 16° is 3.13, and at 24.5° and 16° 

 is 2.86. Again both of the coefficients conform closely to theo- 

 retical demands, and the fact that they are slightly higher than the 

 average coefficient for the data given above is in accord with the 

 results of experiments on other physiological processes — it being 



