12 
BULLETIN 
U. S. DEPARTMENT OF AGRICULTURE. 
umns. These figures are based on a number of actual counts and 
illustrate the effect of a difference of 18° on the multiplication of 
bacteria. If the milk had contained at the beginning 1,000 bacteria, 
the part held at the lower temperature would have contained at the 
end of 24 hours only 4,100 bacteria, while the other would have con- 
tained at the same stage 6,128,000. Table V, from Bulletin 133 
(Extension Bulletin 8) of the agricultural experiment station of 
Nebraska, illustrates the importance 
peratures. 
of holding cream at low tern- 
Table IV. — Multiplication of bacteria 
in milk held at different temperatw 
'es. 1 
Milk held at— 
Relative number of bacteria held at— 
hours. 
6 hours. 12 hours. 
24 hours. 
48 hours. 
50°F 1 1.2 
68° F 1 1.7 
1.5 
24.2 
4.1 
6,128 
6.2 
357, 499 
1 Rogers, Lore A. Bacteria in milk. U. S. Department of Agriculture, Farmers' Bulletin 490. 
Washington, D. C. 
Table Y. — The effect of temperature on the growth of bacteria in cream. 
Temperature of cream. 
Time 
held. 
Number of 
bacteria 
per c. c. 
Temperature of cream. 
Time 
held. 
Number of 
bacteria 
per c. c. 
°F. 
32 
Hours. 
10 
10 
10§ 
3,300 
11,580 
15, 120 
°F. 
70 
Hours. 
11 
11 
11* 
188,000 
2,631,000 
50 
80 
60 
90... 
4,426,000 
THE INFLUENCE OF TIME ON THE BACTERIOLOGICAL FLORA OF MILK. 
The influence of temperature and time bear certain definite rela- 
tions to each other; hence, a study of one necessarily includes a study 
of the other. Table XI serves to illustrate the effect of time as well 
as temperature on the keeping qualities of milk. If the table is read 
downward we note the effect of temperature and if read across the effect 
of time. When milk is first drawn from the cow it usually contains 
bacteria, even though it is produced under sanitary conditions, and 
if held at the ordinary temperature of the surrounding air in a short 
while the bacteria will grow and increase in numbers so rapidly that 
when such milk reaches the consumer it will contain many thousand 
bacteria per cubic centimeter. 
Conn furnishes an example of milk giving the f olio wing results : 
Bacteria per c. c. 
Milk drawn at 59° F 153, 000 
After 1 hour 616, 000 
2 hours 539, 000 
4 hours 680, 000 
7 hours 1, 020, 000 
9 hours 2, 040, 000 
24 hours 85, 000, 000 
