262 PATHOGENIC BACTERIA IN MILK 



the milk of the specific bacillus of any human disease, but from the 

 incidence of the outbreaks amongst those having a community of 

 milk supply, and from the more or less direct evidence of the con- 

 tamination of that milk supply by patients suffering from the 

 disease in question. Secondly, since 1881 there has been the added 

 inquiry as to the communicability of zymotic disease from the cow 

 itself. About these two matters, and particularly about the second, 

 there has been not a little controversy. To the different views 

 which have had their supporters, reference will be made in the 

 present chapter. It will, however, be necessary to restrict our 

 review in this connection to scarlet fever and diphtheria, and these 

 matters will be treated of under the diseases in question. 



Finally, it must not be forgotten that in the first two decennial 

 periods of milk epidemiology, investigators lacked two powerful in- 

 struments of inquiry which we possess to-day, namely. Notification 

 and Bacteriology. With the former, it is practically impossible to con- 

 ceal disease on a large scale. Not only has notification given a more 

 exact record of cases of infectious disease, but it has also advanced the 

 accuracy of diagnosis. By the latter, bacteriology, we have learned 

 something of the etiology of bacterial diseases and of the flora of milk. 



Chief Characteristics of Milk-borne Epidemics 



Owing to the variety of circumstances and conditions which 

 affect the question, it is not possible to formulate any general 

 laws, the fulfilment of which may be recognised, on all occasions 

 when disease is conveyed by milk. The milk trade itself is 

 becoming more and more complex, especially in towns, and hence 

 it happens that simple outbreaks of disease, derived from, say a 

 single milk supply, are rare. Still more complex are the circum- 

 stances and conditions surrounding the consumer. In every case 

 there are manifold idiosyncrasies and susceptibilities in addition 

 to a bewildering number of trifling external differences between 

 individuals even in the same families or households, and the 

 manner and degree in which they respond to various infectious 

 diseases. From this it follows that no two epidemics are alike. 

 To this has further to be added, the disability due to an incomplete 

 and, what may be called provisional, knowledge both of the bacteri- 

 ology of milk and of the ways and means by which it conveys 

 disease. Hence, we can lay down no clear and definite signs which 

 never vary, no hard and fast laws of pathognomic significance. We 

 desire it, therefore, to be understood, that what follows is of the 



