469 
These experiments were originally designed to demonstrate the 
presence of a germicidal substance in solution, but the results again 
show that the action is in part due to agglutination. As far as the 
restraining action is concerned, the results resemble a feeble antiseptic 
rather than a germicide. 
THE EFFECT OF HEATING AND FREEZING. 
The effect of heat varies with the micro-organism. The power to 
restrain B. lactis aerogenes is weakened and destroyed before that for 
typhoid. Thus, 55° C. for thirty minutes or 60° C. for twenty minutes 
markedly alters or destroys the power of milk to restrain the B. lactis 
aerogenes , while this degree of heat shows little influence as far as B. 
typhosus is concerned. 
Freezing milk for ten minutes apparently does not influence its 
germicidal power. Freezing the milk for forty-eight hours before 
inoculating it has no influence upon its restraining action as far as the 
typhoid organism is concerned, but destroys this power for B. lactis 
aerogenes. 
In the freezing experiments a small quantity of the milk w as frozen 
solid by a mixture of salt and ice and kept in this condition for the 
times stated. It wras then cautiously thawed and inoculated wdth the 
micro-organisms to be tested. 
The reason for selecting the temperatures used in Table No. 20, viz, 
55° C. and 65° C., was to differentiate the true bactericidal from the 
agglutinating substances, based upon similar work upon blood serum. 
Table Xo. 19. — Milk from a healthy cow {No. 2 ) inoculated 2 hours after milking. 
% 
Bacteria 
per loop at 
once after 
inocula- 
tions. 
Bacteria 
per loop 
after 8 
hours 
at 37° C. 
B. typhosus in milk first frozen 10 minutes 
(«) 
800 
B. typhosus in milk heated do 60° C. 20 minutes 
8,000 
12,000 
B. tvphosus in milk heated to 80° C. 20 minutes 
18,000 
a b 380, 000 
B. tvphosus in the whole raw milk 
3,500 
1,200 
B. typhosus in sterilized milk (control) 
16,000 
® b 160, 000 
B. lactis aerogenes in milk first frozen 10 minutes 
10,000 
1,700 
B. lactis aerogenes in milk heated to 60° C. 20 minutes 
11,000 
a b 50, 000 
B . lactis aerogenes in milk heated to 80° C. 20 minutes 
20,000 
a b 400, 000 
B. lactis aerogenes in the whole raw milk 
5, 400 
33 
B. lactis aerogenes in sterilized milk (control) 
36,000 
a b 500, 000 
Original milk 
19 
42 
® Innumertabie. 
b About. 
/ 
