6 
BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 
would rarely be met with under commercial conditions. The milk 
was produced in a dirty barn and placed in utensils handled in the 
following manner: The milk was poured out of the utensils promptly 
after milking, but the drippings were not removed till 24 hours later, 
when the utensils were washed in lukewarm water without the use of 
either brush or washing powder. During the time that the utensils 
were allowed to remain unwashed they were exposed to an atmos- 
pheric temperature averaging 85° F. (29.5° C.) Reference to Table 2 
shows that in the six samples examined both the total and colon 
counts were very high in the fresh milk, and that most of the organ- 
isms of the colon-aerogenes group were of the B. aerogenes type, al- 
though a considerable percentage consisted of the B. coli type. 
These figures merely show that both types of organisms may be in- 
troduced through unsterilized utensils, but it must be clearly under- 
stood that the high total and the high colon counts obtained under 
this abnormal condition are very extreme, as will be subsequently 
seen. Milk may become heavily contaminated in this manner with 
both the B. coli and B. aerogenes types. 
Table 2. — Bacillus coli and B. aerogenes contamination due to filthy utensils. 
Sample 
No. 
Total 
count. 
Colon 
count. 
B. Coli. 
B. aero- 
genes. 
1 
2 
3 
4 
5 
6 
Per c. c. 
18,900,000 
25, 300, 000 
16,500,000 
28,200,000 
33, 000, 000 
17, 200, 000 
Per c. c. 
5, 200, 000 
3, 600, 000 
1,190,000 
6,700,000 
1, 620, 000 
340,000 
Per cent. 
31 
35 
38 
8 
2 
14 
Per cent. 
69 
65 
62 
92 
98 
86 
Organisms of the colon-aerogenes group may also be introduced 
into milk through the air. In this connection it is necessary to make 
some distinction between contamination by relatively large particles 
of feces which drop directly into milk from the body of the cow and 
very fine particles of dry feces and feed carried by the air in the form 
of dust. Under average conditions it is practically impossible to 
eliminate this kind of dust. An examination made of the air at 
various places as shown in Table 3 shows the nature of such dust 
infection. Twenty liters of air from each location was drawn through 
20 cubic centimeters of sterile milk. A determination of the colon- 
aerogenes group was then made immediately by plating the milk on 
litmus-lactose-asparagin agar, 1/100 of a cubic centimeter being the 
lowest dilution made. It may be seen that in the fresh milk only two 
samples showed the presence of the colon-aerogenes group, and both 
were of the B. aerogenes type. The milk was examined again after 
24 hours at 70° F. (21.1° C), when all but 5 out of 22 samples showed 
the presence of organisms of the colon-aerogenes group. 
