186 MICROBIOLOGY 



delivered for transportation. If, however, its temperature is, 

 allowed to rise to 60 F. or above during the time it is in 

 transit, the bacteria present will multiply, producing acids and 

 by-products, so that when delivered the milk may have .become 

 markedly, if not seriously, changed. As care of the milk re- 

 quired in the course of transportation is simply to have it put 

 in clean cans and kept at a low temperature, there is no reason 

 why milk cannot be shipped hundreds of miles and be delivered 

 in a perfectly sweet and wholesome condition. The details of 

 the methods for keeping it at a low temperature must, of 

 course, be worked out by shippers generally as they have suc- 

 cessfully been by some milk companies. The only requisite 

 that the consumers need demand in the transportation is that 

 the low temperature be maintained. 



Significance of bacteria in milk. The significance of 

 bacteria may be summarized as follows: (1) The non-patho- 

 genic bacteria cause various changes in milk such as the lactic 

 and butyric fermentation, bitter milk, ropy milk, etc. Some- 

 times certain species of bacteria become localized in the udder 

 from which they get into the milk where they cause disagree- 

 able taints or odors in the milk itself or in its products. Some 

 of these may produce morbid conditions indirectly by the 

 action of their by-products. (2) The pathogenic bacteria if" 

 present will produce their respective diseases in the susceptible 

 consumer. The danger from external contamination is shown 

 from the fact that there were reported in 1895, 138 epidemics 

 of typhoid, 74 of scarlatina and 28 of diphtheria that were 

 traced to milk supplies. 11 Tubercle bacteria that escape with 

 the milk from cows which have tuberculous udders often infect 

 calves and pigs. The feeding of separated milk from cream- 

 eries receiving infected milk is one of the most important 

 methods of spreading tuberculosis among cattle. 12 It is also - 

 the source of much tuberculosis among swine. 



11 Busey and Kober. Report of the Commissioner of the District 

 of Columbia, 1895. 



12 Russell. Bulletin No. 143, Univ. of Wis. Agric. Exp. Station, . 

 1907. 



