MILK-BORNE INFECTIONS 



SINCE about the middle of last century, evidence has rapidly 

 accumulated that milk not infrequently is a vehicle for carrying 

 infection. It has been shown that there are many ways in which 

 milk may be contaminated with bacteria, and it is, therefore, 

 not surprising that sometimes pathogenic germs gain access. 

 Milk is a suitable medium for growth of many micro-organisms, 

 including forms of pathogenic bacteria, while water does not favor 

 the growth of this class of germs. Since milk is frequently han- 

 dled in a careless manner and not cooled sufficiently, pathogenic 

 bacteria that enter it not only live but in many cases multiply 

 at a considerable rate. Therefore, epidemics following the use 

 of infected milk or infected milk products chiefly ice-cream and 

 butter have occurred. And when the enormous quantity of 

 milk and milk products consumed is taken into account it is 

 almost surprising that the number of epidemics due to these 

 foods is not greater than it actually is. In 1899, according to 

 the twelfth census of the United States, 740,000,000 gallons of 

 milk 'were consumed in this country. This amount averages 23 

 gallons for each person and does not include milk used for man- 

 ufacture of butter, cheese, and other dairy products. Since that 

 time the consumption has, of course, increased materially. 



Unfortunately the frequency of milk-borne infections in rela- 

 tion to those due to other causes has not been carefully studied. 

 For example, in the literature statements appear that 10 to 25 

 per cent, of all typhoid epidemics are milk-borne, but accurate 

 statistical evidence to this effect is lacking. The layman is only 

 too frequently impressed with the number of epidemics that have 

 followed in the Wake of milk consumption, and it cannot be de- 

 nied that there is much ground for guarding milk-supplies against 

 contamination with disease germs. This, however, is a difficult 

 undertaking, because, as has been pointed out in an earlier chap- 

 ter, disease germs are difficult to isolate from milk, chiefly for the 

 following reasons : 



1. The relative number of pathogenic bacteria, as a rule, is 

 small in comparison with the number of saprophytes. Conse- 

 quently, high dilutions of milk are necessary in the preparation 

 of plates in order to bring the number of colonies to a reasonable 

 figure for study. As a consequence, colonies of pathogenic bac- 



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