82 
justifiable, therefore, to assume that if 60° C. for twenty minutes is 
sufficient to destroy the infectiousness of such milk when injected 
into the peritoneal cavity of a guinea pig, am^ ordinary market milk 
after such treatment would be safe for human use by the mouth so 
far as tubercle bacilli are concerned. 
The lesions produced by a large mass of dead tubercle bacilli may be 
distinguished by their extent rather than by their character. In doubt- 
ful cases secondary inoculation is the onl}^ trustworthy method of 
determining whether the bacilli are alive or dead. The tuberculin 
test does not differentiate between the live and dead tubercles. Three 
guinea pigs out of eight having lesions produced by dead tubercle 
bacilli (killed at 100° C.) died as the result of the subcutaneous inocu- 
lation of 2 c. c. tuberculin (O. T.). 
The evidence is plain that milk heated to 60° C. and maintained at 
that temperature for two minutes will kill the typhoid bacillus. The 
great majority of these organisms are killed by the time the temper- 
ature reaches 59° C., and few survive to 60° C. 
The diphtheria bacillus succumbs at comparatively low tempera- 
tures. Oftentimes it fails to grow after heating to 55° C. Some occa- 
sionally survive until the milk reaches 60° C. 
The cholera vibrio is similar to the diphtheria bacillus so far as its 
thermal death point is concerned. It is usually destroyed when the 
milk reaches 55° C. ; only once did it survive to 60° C. under the condi- 
tions of the experiments. 
The dysentery bacillus is somewhat more resistant to heat than the 
typhoid l)acillus. It sometimes withstands heating at 60° C. for five 
minutes. All are killed at 60° C. fof ten minutes. However, the 
great majoritv of these micro-organisms are killed by the time the 
milk reaches 60° C. 
So far as can be judged from the meager evidence at hand, 60° C. 
for twenty minutes is more than sufficient to destroy the infective 
principle of Malta fever in milk. The M. rnelitensis is not destroyed at 
55° C. for a short time; the great majority of these organisms die at 
58°, and at 60° all are killed. 
Milk heated to 60° C. and maintained at that temperature for twenty 
minutes may, therefore, be considered safe so far as conveying infec- 
tion with the micro-organisms tested is concerned. 
