204 Journal of Agricultural Research voi. xvii, no. s 



the vitality of the worms. At 53° C. he found the vitality of the worms 

 slightly reduced, but the results were variable. At 54° C. there was a 

 further reduction in vitality, but meat which was heated to 55° C. and 

 maintained at that temperature for 15 minutes was not capable of 

 producing an infection. 



EXPERIMENTAL WORK 



Experiments by the present writers on the effects of heat on the larvae 

 of Trichinella spiralis have been made with meat containing encysted 

 larvae as well as with larvae freed from their capsules by artificial diges- 

 tion. In the former case there is more or less difficulty in obtaining accu- 

 rate data, since the temperature in the interior of the meat does not neces- 

 sarily correspond to the temperature of the medium in vvhich it is heated. 

 This difficulty may be overcome, however, if small pieces of muscle tissue 

 are used and if the temperature is raised gradually. In experiments on 

 larvae freed from their cysts by artificial digestion more accurate deter- 

 minations can be made, since the temperature of the medium is an excel- 

 lent index to the temperature of the parasites themselves. From a com- 

 parison of the results obtained by the two methods definite conclusions 

 regarding the thermal death point of the larvae may be drawn. 



OBSERVATIONS ON THE SURVIVAL OF DECAPSULED LARV^ IN 



VARIOUS MEDIA 



In comiection with experiments on the effects of heat upon decapsuled 

 larvae, the question of their sur\nval in various media following artificial 

 digestion is important, since such experiments are complicated by the 

 factor of abnormal environment, and results obtained might not corre- 

 spond with those obtained in experiments in which the parasites are sub- 

 jected to heat while still inclosed in their capsules in pieces of meat. En- 

 cysted trichinae may be kept alive for many months and may still be 

 viable in meat that has become badly decomposed. Although decap- 

 suled larvae are unlikely to survive as long as encysted larvae, they can be 

 kept alive for considerable periods of time. In a paper by the senior writer 

 (Ransom, 11), it has been shown that decapsuled larvae may retain their 

 normal activity and appearance when kept in tap water or 0.6 per cent 

 salt solution at a temperature of about 20° C. for a period of from 10 days 

 to two weeks or more, and that they have been kept alive and very active 

 for as long as 1 1 days in 2 per cent salt solution. On the other hand, at a 

 temperature of 38° decapsuled larvae kept in tap water became inactive 

 within a few hours, whereas when kept in 0.6 per cent salt solution at the 

 same temperature for the same length of time they suffered no apparent 

 injury. 



Further observations have been maae by the junior writer which show 

 quite clearly that the longevity of the larvae after artificial digestion de- 

 pends upon both the medium in which they are kept and the temperature 



