274 PATHOGENIC BACTERIA IN MILK 



perhaps in enormous numbers, in the food, untasteable, invisible, 

 and imperceptible. But when introduced into the blood and tissues 

 of the body, under favourable conditions of pabulum, moisture, 

 and temperature, it proceeds at once, with greater or less rapidity, 

 to multiply and pass throughout the body, producing its toxins. 

 It is incubating, and the condition is an infection. Now, in milk 

 epidemics, we may get one or other of these modes of invasion. In 

 some cases the disease follows almost immediately after the intro- 

 duction of the causal agents — the moment of infection — with such 

 rapidity that the condition is allied to an intoxication. In other 

 circumstances the events take an ordinary course, and an infection 

 follows with a normal length of incubation period. 



Various attempts have been made to explain the phenomenon 

 of a short incubation period in milk-borne disease. Some have 

 attributed the condition to the ready attachment of milk to the 

 mucous membrane, and the early absorption of the milk globules 

 into the lymph-stream, or the easy digestibility of milk. Others 

 have considered the human element as playing a large part. 

 Women and children, it is urged, are readily susceptible. But, in 

 fact, neither of these hypotheses is adequate to the phenomenon. 

 It has also been suggested that fatigue plays an important part in 

 shortening the incubation period. 



As we have seen, those diseases having a very short incubation 

 period, such as diphtheria or scarlet fever, almost take the form of 

 intoxications. That is to say, the symptoms produced are largely 

 due to products of organismal activity. Hence a seemingly 

 more reasonable explanation is surely to be found in the theory 

 that the pathogenetic organisms present in the milk have found in 

 it a favourable nidus for development and maturation. Milk is, as 

 we have seen, an almost perfect pabulum ; there is also moisture, and 

 in freshly drawn milk a favourable temperature. We know as a fact 

 that bacteria multiply with almost incredible rapidity in fresh milk. 

 Is it not possible that, under these circumstances, individuals con- 

 suming such milk imbibe not only organisms but toxins and other 

 products already produced by them ? Such a condition of things 

 would tend to shorten the incubation period. 



There is another point to be borne in mind in this relation. 

 We have already seen that persons become infected in proportion 

 to the amount of the contaminated milk which they drink. But 

 we may now go a step further. In 1897 an outbreak of typhoid 

 fever was traced to the milk supply. Amongst other things it was 

 found that the attack rate was highest among the people who had 



