DETECTION OF MILK EPIDEMICS. 123 



ever, cannot be done by bacteriological means. The cause of 

 scarlet fever is unknown and, of course, can not be detected 

 in milk. The bacteria that produce typhoid fever and diph- 

 theria are, however, well known, but it is as yet practically 

 impossible to study market milk with the expectation of 

 detecting the presence of these organisms. The large num- 

 ber of bacteria in ordinary milk makes the detection of these 

 two bacilli practically impossible. But, aside from this diffi- 

 culty, there is another one that makes it quite hopeless to use 

 bacteriological methods in determining the source of such 

 an epidemic. When milk has been the cause of a typhoid 

 epidemic the disease does not follow until one to four weeks 

 after the infected milk has been distributed. It requires 

 some time after this for the persons who are investigating 

 the matter to trace the epidemic to a milk supply. Conse- 

 quently the milk is not thrown under suspicion until some 

 weeks after the milk has begun to distribute pathogenic 

 germs. By that time it is most likely that the milk from the 

 same source will no longer be contaminated with the typhoid 

 bacilli. The contamination of the milk of any farm with the 

 typhoid bacillus is commonly a fleeting one, due to excep- 

 tional conditions, and the milk is thus infected with the 

 germs for a few days only. How long the contamination 

 may continue cannot be stated, but it will rarely last many 

 days. The examination of the milk from such a source after 

 the epidemic has appeared would usually be quite fruitless, 

 for the milk, by the time it is placed under the observa- 

 tion of a bacteriologist, will probably, in the majority of 

 cases, be quite free again from the special contaminating bac- 

 teria. As a result, detection of milk epidemics by bacterio- 

 logical methods is, at present at least, quite impossible. 



The evidence, therefore, that milk is the source of an epi- 

 demic must be derived from other methods of investigation. 

 The method by which an investigation is carried on is toler- 

 ably simple. If there is a violent epidemic of typhoid or 



