128 BACTERIOLOGICAL METHODS 



bacteria may enter the milk causing the very characteristic fer- 

 mentation changes resulting in the formation and liberation of bu- 

 tyric and propionic acids from the splitting of lactose. Butyric acid 

 milk has a very disagreeable odor. Various bacteria cause dis- 

 eases of milk as blue milk and ropy milk. 



In some American cities the routine examination of milk for 

 B. coli is regularly adopted. The results in Baltimore have shown 

 the presence of this bacillus in 25 per cent, of o.ooi cc. quantities 

 of the milk in the winter time and 75 per cent, during the summer. 

 It would appear that three positive tests out of a total of five 

 from o.ooi cc. quantities of milk, would indicate the danger point 

 as to quality. For making plate counts of milk bacteria, lactose- 

 litmus-agar should be used in order to differentiate between 

 acid formers and non-acid formers. 



In most communities the milk streptococci are considered 

 objectionable, as they belong to the group of pus-forming organ- 

 isms. It is frequently found that a high streptococcus count goes 

 with a high leucocyte count and the two are corroborative of the 

 existence of some severe inflammatory condition of the udder or 

 milk ducts. There is fairly conclusive evidence that the hemo- 

 lytic milk streptococci are frequently causative of more or less 

 severe and even fatal intestinal diseases among children, especially 

 during the hot summer weather. It is also fairly well proven that 

 some of the throat and mouth infections of children are traceable 

 to the staphylococci and streptococci of milk. The problem of 

 tuberculous milk is of lesser importance to the food bacteriologist 

 because the health authorities of the land have this matter under 

 jurisdiction. It is criminally unlawful to market milk from tuber- 

 cular cows. Ravenel states that approximately 20 per cent, of 

 the clinical cases of tuberculosis are of the bovine type and milk 

 from tuberculous cows continues to be a very serious menace to 

 the public health. It would be of the greatest value if some simple 

 and practical micro-chemical laboratory test for tuberculous milk 

 could be worked out. We would suggest this as one of the very 



