268 



PATHOGENIC BACTERIA IN MILK 



Dr King Warry, the medical officer of health, investigated this point 

 of incidence according to consumption, with the following result : — 



Here, again, the same clear result is demonstrated, and we think 

 it may be set down as a principle almost always present in milk-borne 

 epidemics, though not always discoverable. And it may be added 

 that the amount of infected milk consumed bears a direct relation to 

 the length of the incubation period, the attack rate, and the severity 

 of the attack. Therefore it is related also to the mortality rate. 



There are some further facts which emerge from a careful 

 study of the records of the milk-borne epidemics dealt with in the 

 present chapter in respect to incidence of infection on milk- 

 drinkers. These facts have reference to the numbers of persons 

 who took the suspected milk in relation to the total number of 

 cases, and the number of families attacked in relation to the 

 number of families supplied by the suspected milkman. We have 

 made a careful study of the available records, and we find that of 

 the persons attacked, the lowest percentage of those who took the 

 implicated milk was : — in scarlet fever 64- per cent, in typhoid fever 

 66 per cent, and in diphtheria 57 per cent. The highest in each 

 case was 100 per cent The average percentage of persons in all 

 the epidemics who took implicated milk out of the total cases was : — 

 in scarlet fever 92-5 per cent, in typhoid 92-4 per cent, and in 

 diphtheria 86-6 per cent. That is to say, if in each disease one 

 hundred persons were attacked, ninety-two, ninety-two, and eighty- 

 six respectively were the numbers of persons who had taken the 

 implicated milk. Or, if we study the incidence on families supplied, 

 we also get instructive returns. In scarlet fever outbreaks the 

 lowest percentage of the families supplied which were invaded 

 with disease was 6, the highest was 100; in typhoid, the lowest 

 incidence of which we have reliable figures was 11, and the highest 

 100 ; in diphtheria, the lowest incidence is represented by 7 per 

 cent, and the highest by 59. That is to say, of one hundred 

 families supplied by the suspected milkman, seven and fifty- 

 nine were attacked, respectively. Or the averages for the same 



