2i6 Journal of Agricultural Research voi. xvii, No. s 



The following experiments to determine the effects of the continued 

 exposure of decapsuled larvae to temperatures below 53° C. were carried 

 out by the junior writer. The larvae in 0.7 per cent salt solution or in 

 Ringer's solution were first heated to a given temperature and then 

 placed in an incubator at the same temperature for a given period. 

 When taken out of the incubator the larvae were kept at room tempera- 

 ture at least an hour before they were examined. 



Experiment 20. — In one test the larvje were all dead after exposure 

 for three hours to a temperature of 48° C, but generally an exposure to 

 a temperature of 48° for less then four hours failed to destroy their 

 vitality. In every case, however, after they were heated four hours at a 

 temperature of 48° they were all uncoiled, having assumed the shape of 

 the figure 6; and they failed to react to heat stimulation. 



Experiment 21. — When exposed to a temperature of 49° C. nearly 

 one-half the larvae in one lot were still alive at the end of two hours. 

 Another lot from a different host animal succumbed to a similar treat- 

 ment, but in no case did a briefer exposure to 49° prove effective. When 

 subjected to 49° for 3X hours all the larvae became completely uncoiled, 

 rigid, and insensitive to thermal stimuli. 



Experiment 22. — At a temperature of 50° to 50.6° C, the vitality of 

 the larvae was completely destroyed after an exposure of i hour and 20 

 minutes. At a constant temperature of 50° an exposure of i K hours 

 proved fatal. 



Experiment 23. — An exposure of one hour to a temperature of 52° C. 

 was sufficient to destroy the vitality of decapsuled larvae. 



From the foregoing experiments it is evident that decapsuled trichina 

 larvae die in a comparatively short time when exposed to temperatures 

 in the neighborhood of 50° C. and that the time required for their de- 

 struction increases as the temperature is lowered. If the results of 

 these experiments are considered in connection with the question of the 

 length of time that decapsuled larvae survive at temperatures ranging 

 below 40°, already discussed in this article, it may be concluded that 

 between limits at which the larvae become altogether quiescent because 

 of the effects of heat on the one hand and of cold on the other their 

 longevity varies inversely with the temperature. It would, however, 

 not be safe to conclude from the experiments just described that exposure 

 of trichina larvae to the temperatures given for the stated periods of 

 time would be sufficient in all cases to destroy the vitality of the para- 

 sites. It is not improbable that in these experiments the larvae had 

 already become som.ewhat exhausted as a result of abnormal activity 

 during the process of artificial digestion, and furthermore it is possible 

 that different lots of trichinae vary considerably with respect to their 

 store of vitality. The following experiments by the senior writer show 

 that the vitality of encysted trichinae as well as that of decapsuled 



