Il8 MILK BACTERIA AND HEALTH. 



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dairy. He impregnates the milk with the bacilli from his 

 throat, and these serve as a source from which the disease 

 may be transmitted through the milk to the consumer. Such 

 a cause of a diphtheria epidemic has been definitely traced. 

 It is possible also that there are other secondary sources of 

 infection, but not much is known about them at present. It 

 has not yet been definitely settled whether the cows them- 

 selves are subject to diphtheria and may have the dis- 

 ease located in such a way that they produce milk which, 

 from the outset, is contaminated with diphtheria organisms. 

 Experiments have indicated that the injection of diphtheria 

 bacillus into cows produces an infection of some sort, and 

 that the infection may show signs of itself in the udder. 

 There is, however, no good reason for believing that the 

 milk produced from such udders contains the virulent diph- 

 theria bacillus. It has been claimed that such milk may pro- 

 duce diphtheria, but the most recent evidence indicates that 

 such a danger does not exist (138, 139). 



Milk may certainly become contaminated with diphtheria 

 bacillus from secondary contamination, and the bacilli are 

 capable of growing and becoming abundant in the milk. 

 Although it is possible, under some conditions, to detect 

 diphtheria bacillus in milk, it is a difficult task and quite 

 impracticable for ordinary purposes of milk testing. That 

 these bacilli have caused certain diphtheria epidemics has 

 been clearly proved, although there is no reason for believing 

 that many of the diphtheria epidemics are traceable to such 

 a cause. It is also uncertain to what extent the milk may 

 be a source of the miscellaneous cases of diphtheria which 

 are found in communities. We must simply look upon milk 

 as one of the possible means of distribution, and in the case 

 of a diphtheria epidemic this must be looked at as one of the 

 possible sources of infection. In the majority of diphtheria 

 epidemics the infection doubtless comes from some other 

 source (direct contagion, school books, etc.), and milk must 



