8 BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 



It is not difficult to explain the presence of bacteria of the aerogenes 

 type in air either inside or outside the barn, for they appear to be 

 widely distributed on grains and other feeds, and in the soil. Rogers, 

 Clark, and Evans (15) in their study of 166 organisms of the colon- 

 aerogenes group occurring on grains, found that 151 were of the B. 

 aerogenes type, while 8 resembled but were not identical with the B. 

 coli type. An examination of many samples of alfalfa, cane, corn, 

 and kafir-corn forage by Hunter (5) at the time of filling the silo 

 showed coli-like cultures ranging in number from 1,000 to 1,000,000 

 per gram. A study of 95 of the organisms isolated from different 

 kinds of silage, and of 15 strains obtained from growing fields of alfalfa 

 and kafir corn showed about 2 1 per cent to be of the B. coli type and 

 79 per cent of the B. aerogenes type, as differentiated by the methyl- 

 red test. 



That coli-like organisms are present in soil has been shown by 

 Johnson and Levine (7), who found them more prevalent in soils upon 

 which crops were growing than in absolutely fallow areas receiving 

 soil treatment. Aerogenes-cloacge types were found to be the pre- 

 dominant coZi-like forms in the soil. 



It is apparent that the B. aerogenes type found in air may be 

 derived from various sources, and it is not inconceivable that the 

 organisms of this type found in market milk produced under clean 

 conditions are the descendants of those introduced into the fresh milk 

 in extremely small numbers by means of air contamination. It is also 

 possible to contaminate milk with organisms of the B. aerogenes type 

 by using unsterilized utensils. 



Having surveyed the various means by which fresh milk is infected 

 with organisms of the colon-aerogenes group it is now possible to 

 answer the question "Do organisms of the colon-aerogenes group 

 indicate the presence of manure in fresh milk ? ' ' The presence of the 

 B. coli type indicates manurial contamination either directly from 

 fecal material which drops into the milk principally from the body 

 of the cow or indirectly through unsterilized utensils. It must be 

 pointed out that the contamination by cow feces represents a much 

 more serious form than that from unsterilized utensils. This state- 

 ment may be explained by the fact that the introduction of cow feces 

 into milk may carry organisms of bovine tuberculosis. Schroeder (19) 

 has shown that cattle having tuberculosis swallow their sputum, and 

 the tubercle bacilli in it pass through their bodies and out into the 

 feces. The contamination of milk through unsterilized utensils 

 represents a condition of careless handling in which there has been 

 growth of the B. coli type in the utensils. While this kind of con- 

 tamination may add as large a number of the B. coli type to milk as 

 the fecal, it would not represent the same possibilities for infection 

 with the bovine tubercle bacillus as does the latter. So far as the 



