HEAT RESISTANCE OF PARAMECIUM 221 



ture fluid inside was about one inch below the level of the water 

 of the bath outside the jar. The mercury bulb of the thermome- 

 ter showing the temperature of the water bath was also placed 

 about one inch below the surface of the w^ater, so that it gave 

 very closely the actual temperature to which the Paramecia were 

 exposed. The culture jar itself was of course kept covered with 

 a glass plate at all times. The constant temperature of 28° 

 was maintained for a period of 27 days. On March 10 the tem- 

 perature was raised to 30°C. and on the 12th to 32°C. After 

 10 days at 32° the temperature was again raised to 34°. After 

 16 days at 34° the temperature was raised on April 7 to 35°, 

 and on April 15 to 36°, at which point it was maintained to the 

 end of the experiment. On April 26 the culture was in very poor 

 condition and very few animals were present. A little dry 

 fresh hay was added to the medium but it did not have any favor- 

 able effect and the strain had completely died out by April 29. 

 " Strain 30-b was used as a check on 30-a, and was kept on a 

 table in a cool room, the temperature of which varied from 12° 

 to 22°C. On April 29, when 30-a had completely died out, 

 30-b was still in good condition, although not as densely popu- 

 lated as in earlier periods of its growth. 



During the course of the experiment the heat resistance of 

 both strains was studied at frequent intervals. The mean of the 

 fatal temperature zone for each experiment was worked out in 

 the usual way and these means are plotted in figure 1. 



Another pure culture, 11-2, was started from an individual 

 isolated on December 11, 1912. This culture was kept at room 

 temperature until February 14, at which time it was transferred 

 to the water bath at 28°C. From that time on until the cul- 

 ture died out (April 25) it wa^ subjected to the same temperature 

 conditions as w^as 30-a. The mean death temperatures of a 

 series of tests with this strain are also plotted in figure 1. Ex- 

 amination of the figure shows that the resistance of the control 

 was by no means constant. There was considerable variation, 

 the means varying from 40.5 to 42.3°C. . The resistance was more 

 irregular and in general slightly higher during the later course 

 of its history than in the earlier experiments. 



