126 MILK BACTERIA AND HEALTH. 



clusively that, in this case, the scarlet fever epidemic .was to 

 be traced back to the source A, which was, therefore, imme- 

 diately placed under suspicion and was investigated by those 

 in charge of the work. In this particular epidemic it was 

 found that upon the farm A there was, at the time when the 

 milk was probably contaminated, a mild case of scarlet fever, 

 so mild as not to confine the patient in bed, and the boy in 

 question was employed in the dairy in handling the milk. 

 This mild case of the disease was followed presently by two 

 more severe attacks of scarlet fever, but the milk infection 

 was regarded as due to the mild case where the individual 

 was employed in the dairy during the sickness. In such an 

 instance as this it is beyond question that the epidemic must 

 be traced to the milk supply and to the particular milk supply 

 marked as A (144). 



It is by no means always possible to trace the source of 

 such an epidemic with the accuracy and satisfaction of the 

 example here given. The milk of different milkmen is so li- 

 able to be exchanged, and people using the milk are so liable 

 to visit each other and consume milk in other houses, or even 

 to borrow milk from each other, that a considerable con- 

 fusion arises. In all milk epidemics it commonly happens 

 that there will be a number of cases that cannot be traced 

 directly to the source in question. Many of these, however, 

 upon strict investigation, can be traced to the same source 

 of infection through the mixing of milk or some other 

 similar method. It is not to be expected, therefore, that 

 every case of the disease in such an epidemic can be traced 

 absolutely to the milk supply in question, but where the large 

 proportion, ninety per cent, or so of the cases, are found to 

 use milk from one source, the inference that this source has 

 been the cause of the epidemic is emphatic. 



It is also evident that such a method of tracing the epi- 

 demic, while perfectly feasible in small communities, where 

 the milk is distributed from individual farms by individual 



