G 



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. — BacillKS coli and B. aerogenes contamination due to filthy utensils. 



Sample 

 No. 



Total 

 count. 



Colon 

 count. 



B. Coll. 



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. 



