394 BACTERIA IN MILK 



Further investigations have shown that Aerobacter aerogenes is not commonly 

 present in human feces, though common in the upper intestine of man. Two early 

 habitat studies of colon organisms isolated from milk were made in England. Hous- 

 ton' determined the characters of 343 cultures of the colon group isolated from milk 

 and found that 221 non-gelatin-liquefying cultures fermented sucrose with the for- 

 mation of acid and gas. This result indicates that Aerobacter aerogenes was at least 

 abundant, though the characters determined were not sufficient to establish the iden- 

 tity of the organism. Orr' used the Voges-Proskauer test on 850 cultures of colon or- 

 ganisms from milk and found 2)2)Z of them to be positive, again indicating that Aero- 

 bacter aerogenes was frequently present. 



Rogers, Clark, and Davis^ have studied a series of colon cultures from milk by 

 more accurate technique and report that the carbon dioxide and hydrogen ratio that 

 occurred with the greatest frequency was approximately 1:1. The amount of gas pro- 

 duced by these cultures was uniformly less than that produced by high-ratio cultures. 

 The amount of acid produced was frequently masked by secondary alkaline fermenta- 

 tions in which the acid was partially or completely neutralized. 



LACTOBACILLI IN MILK 



The long-rod lactic acid bacteria also form an important group in their relation- 

 ship to milk. They have even more important relationships to fermented milk prod- 

 ucts and will therefore not be discussed at this place. The most important species 

 are Lactobacillus bulgaricus (Grigoroff) Holland and the closely related, if not identical, 

 L. helveticum (Orla- Jensen) Bergey {Bacillus casei e Freudenreich). Lactobacillus 

 acidophilus (Moro) Holland is closely related to these species, but is regarded as dis- 

 tinct by those who are most competent to judge the matter. 



■ Houston, A. C: The Bacteriological Examination of Milk, London Co. Council, No. 933. 1905. 

 ^ Orr, T. : Investigation as to the Contamination of Milk. Co. Bor. Councils of Bradford, Hull, Leeds, 

 etc. {Beverly). 1908. 



3 Rogers, L. A., Clark, W. M., and Davis, B. J.: /. Infect. Dis., 14, 411. 1914. 



