842 
Journal of Agricultural Research 
Vol. V, No. 18 
were observed in meat exposed for 14 and 18 days (2 and 3 per cent, 
respectively), these were very sluggish. Furthermore, none of the test 
rats in this series became infested. 
The results of the three sets of experiments just cited demonstrate 
quite clearly that a temperature of io° F. is more effective in destroying 
the vitality of trichinae than a temperature of 15 0 , and that a tempera¬ 
ture of 5 0 is still more effective, illustrating the general rule established 
by the investigations recorded in the present paper, that within certain 
limits the effect upon the vitality of trichinae becomes more pronounced 
as the temperature of refrigeration is lowered. It has also apparently 
been established that the increase in effectiveness is not uniform with 
the decrease in the temperature, but that somewhere in the neighborhood 
of io° a critical point is reached, below which there is a sudden increase 
in the effectiveness of refrigeration. 
Summarizing the results of the various experiments with a view to 
their practical application, inasmuch as very few trichinae have been 
found to survive an exposure of more than 10 days to a temperature of 
5 0 F., or lower, and as the few surviving have shown only very slight 
activity, and as, moreover, trichinous meat exposed to temperatures of 
5 0 or lower has rarely produced infestation, and has never (in repeated 
trials) produced infestation when the period of exposure was more than 
10 days, it may be concluded that meat exposed to a temperature not 
higher than 5 0 for a period of 20 days will no longer contain viable 
trichinae, 10 days in this 20-day period being allowed as a margin of 
safety. It may be further concluded that, so far as our present knowl¬ 
edge goes, temperatures of io° and higher are too uncertain in their 
effects upon the vitality of trichinae to justify the use of refrigeration at 
such temperatures as a means of rendering trichinous meat innocuous. 
CHANGES PRODUCED IN TRICHINA LARVM BY EXPOSURE TO DOW TEMPERATURES 
Low temperatures (15 0 F. and lower) not only destroy the vitality of 
some or all of the trichinae which a're exposed to those temperatures but 
they produce changes in the tissues of the parasites, which are apparent 
under the microscope. These changes in appearance are associated with 
reductions in the activity of the trichinae and with losses in their vitality. 
Trichinae from artificially digested unfrozen meat when examined under 
the microscope in water, or preferably in a physiological salt solution 
are found to be tightly coiled, becoming very lively when they are 
warmed to body temperature and continuing their lively movements as 
the temperature increases up to about 50° or 52 0 C. when they become 
sluggish and finally cease movement and die when the temperature rises 
a few degrees higher. The esophageal cellular body of the normal 
trichina has a bright yellowish brown color, and exhibits a certain granu¬ 
lation of the protoplasm; the nuclei of the cells are apparent as small, 
