VI DISEASES OF THE COW 121 



Of course, tuberculosis is not included in this hypothesis. The 

 first conclusion is more capable of proof than the second, and may 

 be accepted without the second being admitted. 



Briefly stated, this view regards the bovine udder and teat 

 lesions, as commonly met with, as of purely bovine origin, and, as 

 such, harmless to man. Occasionally, either as an invasion super- 

 added upon the original bovine lesions, or as a primary infection of 

 the milk organs, there is a local infection with organisms of human 

 origin. In such cases the conditions present may be decidedly 

 prejudicial to man. In other words, the cow, in this class of infec- 

 tions, is only potentially pathogenic to man when it acts as a 

 passive carrier of or is actively infected with organisms of human 

 origin. 



The known facts fit in with this, hypothesis : 



I. It is clear that the great majority of bovine udder and teat 

 lesions are not harmful to man. As evidence of this we have in 

 the first place the striking disproportion between the prevalence of 

 udder and teat lesions and the recorded outbreaks of human disease 

 ascribed to these conditions. Even allowing for a large number of 

 unrecorded outbreaks and numerous individual cases of illness, the 

 disproportion is very marked. In the second place, the bacteriological 

 investigations recorded above have proved that the commonest type 

 of mastitis is not harmful to man in a healthy condition, and probably 

 not when debilitated. The evidence of the innocuousness of the 

 ordinary type of bovine mastitis is added to by the demonstration 

 of the streptococci causing the condition in abundance in the milk 

 of the clinically unafTected quarters — milk which must, therefore, 

 have been repeatedly added to the vended milk. 



II. There is reliable epidemiological evidence connecting at 

 least some sore throat and other human disease outbreaks with 

 affections of the bovine milk organs. The descriptions of these 

 outbreaks in Chapter V. may be referred to for such evidence. 



III. There is clear evidence that organisms of undoubtedly 

 human origin can in certain cases infect the milk organs of 

 bovines. 



The diphtheria instances already recorded offer the most 

 striking evidence of this, because this organism can be readily 

 identified ; if the scarlet fever organism could be identified with equal 

 facility, it is probable that similar evidence for that disease would 

 be forthcoming. The outbreak of Dean and Todd is particularly 

 conclusive, since they proved that there was a separate bovine 

 eruption, with the diphtheria bacilli present as a second superadded 

 infection. Klein and Abbott have both demonstrated that diph- 

 theria bacilli, inoculated into calves and cows, could be recovered 

 at the site of inoculation for some time. 



Certain of the writer's goat inoculation experiments are very 



