BACTERIOLOGY OF WATER AND MILK 181 



in number depends largely upon the care of the cows and the 

 precautions taken in handling the milk. Certified milk sold in 

 New York City must not contain over 30,000 bacteria per 

 cubic centimeter. Park 6 states that the milk dipped and sold 

 at the groceries sometimes contained as high as 80,000,000 bac- 

 teria per cubic centimeter. 



Species of bacteria in milk. Conn, Esten and Stocking 7 

 in their classification and description of dairy bacteria have 

 given 145 species that have been isolated from milk. They 



o 





' 



fSsWfe- 



/O^V^O % *JiV *lQ dark ones are various bacteria. 



Fig. 43. Cover-glass prepara- 

 tion of market milk. The light 

 bodies are fat globules and the 



point out, as did Jordan for water bacteria, the difficulty of 

 identifying species. Several of those they describe are con- 

 sidered type species possessing a greater or less number of 

 varieties. Thus Bact. lactis acidi, the common cause of souring 

 of milk, seems to have many varieties. 



Milk sometimes becomes very bitter owing to the products 

 of certain bacteria multiplying in it. Weigmann, Conn and 

 Freudenreich have isolated and studied a number of such 

 species. A "blue" color is a peculiar condition of milk caused 

 by a single species of bacteria (Pseudomonas syncyanea), al- 

 though it possesses a number of varieties. Slimy or ropy milk 

 is another of the many undesirable conditions brought about 



'Park. The New York University Bulletin of the Medical Sci- 

 ence, Vol. I (1891) p. 1. 



7 Conn, Esten and Stocking. Report of the Storrs (Connecticut) 

 Agricultural Experiment Station, 1906. 



