Aug. IS. 1919 Effects of Heat on TrichitKE 215 



The results obtained from the experiments in which pieces of trichin- 

 ous meat were heated agree with the results of those in which the larv^ae 

 were first freed from their cysts by artificial digestion and then heated in 

 water or physiological salt solution. The larvae are killed if the meat is 

 gradually heated to a temperature of 55° C, though some may escape if 

 the temperature rises rapidly to 55° and soon falls again. They may 

 survive a temperature of 54°; but meat which has been exposed to a 

 temperature of about 53°, gradually attained, is likely to be non- 

 infective. 



It may be concluded that meat which has been heated so that the tem- 

 perature throughout reaches 55° C. (131° F.) will be innocuous so far as 

 concerns the possibility that persons eating such meat will become 

 infected with trichinae, inasmuch as under ordinary conditions of cooking 

 the rise of temperature will be gradual enough to insure the destruction 

 of the parasites if the temperature of the meat actually reaches 55° C. 

 or higher. Under the regulations of the Bureau of Animal Industry the 

 minimum temperature that must be attained throughout all portions 

 of pieces of pork or products containing pork that are cooked in estab- 

 lishments operating under federal meat inspection has been fixed 

 somewhat higher than 55° C, namely 137° F. (58.33° C), which allows 

 a margin of safety of several degrees above the temperature that has 

 been shown by our investigations to be fatal to trichinae. 



THE EFFECTS UPON TRICHINA OF CONTINUED EXPOSURE TO HEAT 

 AT TEMPERATURES BELOW THE THERMAE DEATH POINT 



It has been shown that trichina larvae are killed by brief exposure to a 

 temperature of 55° C, gradually attained; and since they will not after- 

 wards resume their activity when thus heated, this temperature may be 

 considered the thermal death point. The vitality of the larvae may be 

 destroyed also by exposure to lower temperatures, provided the appli- 

 cation of heat is long enough continued. In the former case it may be 

 assumed that death results from irreversible coagulations of the proto- 

 plasm, in the latter case either as the result of coagulation changes which 

 become irreversible if the heat acts for a sufficient period, or as the result 

 of exhaustion following excessive activity to which the larvae are stimu- 

 lated by heat. We may, therefore, distinguish three ranges of lethal 

 temperatures: The highest, in which death comes quickly from rapid 

 and irreversible coagulations of the protoplasm; an intermediate range, 

 in which death results probably from somewhat similar coagulation 

 changes, changes, however, from which the parasites may more or less 

 completely recover if the temperature is lowered before death occurs; 

 and the lowest range, in which death is apparently brought about by 

 exhaustion from increased activity. 



