HEAT RESISTANCE OF PARAMECIUM 223 



In the case of 30-a, which was growing in practically the same 

 medium as the control, we see a much greater fluctuation. The 

 mean death temperatures for this race vary" from 38.5 to 43.4°C. 

 After one week at 28° the resistance decreases and is lower than 

 at the beginning but after February 27 the resistance increases 

 again and the general trend of the line is gradually upward. 

 After the temperature was raised to 34°C. the resistance of this 

 strain remained rather high, being in general from 1 to 2.5° 

 above its initial resistance. However, the highest mean was only 

 1° above the highest mean for the control culture. 



Several experiments with strain 11-2 before it was put in the 

 water bath gave an average mean fatal temperature of 40.5°C. 

 As soon as this culture was subjected to the higher temperatures 

 of the water bath we find that the resistance increases and re- 

 mains at least 1° higher than the initial resistance and at times 

 is more than 2° higher. 



The mean death temperatures of both 11-2 and 30-a at times 

 approached 43° and sometimes exceeded it, while, as pointed 

 out above, the death temperature of the control, 30-b, never 

 exceeded 42.3°. However, this increased resistance of those 

 strains growing at the higher temperatures was not maintained 

 for any considerable period, and it is hard to see that any de- 

 cided effect was produced. 



SUMMARY 



1. The effects of certain salt solutions on the heat resistance of 

 Paramecium caudatum were tested. Two pure lines of Paramecia 

 were used; one growing in a medium of decided alkaline reaction, 

 and the other in a slightly acid medium. Experiments with the 

 race from the alkaline medium showed that M/lOO and M/50 

 NaCl, M/3000 CaCL, and M/50 KNO3 exerted a marked pro- 

 tective action. The greatest increase was noted in a solution of 

 M/lOO NaCl to which a little CaClo had been added. Distilled 

 water also was found to increase the heat-resisting powers of this 

 race. 



