PATHOGENIC ORGANISMS IN MILK 171 



tuberculous milk, and sometimes observations made by different 

 observers have appeared contradictory. In connection with this 

 subject it is necessary to bear in mind that the incidence of 

 tuberculosis in cattle, and consequently the incidence of bovine 

 tuberculosis in man, varies greatly in different parts of the world, 

 the reason for this having not yet been elucidated. Further, 

 the bovine type of the bacillus probably does not produce such 

 a fatal type of disease in man as does the human type. From 

 this it follows that observations as to the strain of bacillus 

 present, made post mortem, must be differentiated from those 

 based on material obtained during life. It may be stated that 

 where much tubercular milk is consumed, the children of the 

 community will in a very considerable proportion of cases show 

 evidence of infection of the mesenteric glands. And again, the 

 diseases of bones and joints and of cervical glands occurring in 

 children will at least in certain localities often yield the bovine 

 type of bacillus. It is manifest that even if, as is probably 

 the case, such affections may be non-fatal, the suffering and 

 mutilation which results cannot be overlooked. So far as present 

 evidence goes, the occurrence of bovine infection after adol- 

 escence is relatively uncommon. It may be said that the argu- 

 ments advanced in support of the view that the consumption 

 of tuberculous milk may have the effect of immunising the 

 individual against human infection, are at present of a purely 

 academic nature. 



Amongst other diseases it has been supposed that pathological 

 changes in the cow's udder may be originated by the causal 

 agent of scarlet fever and of diphtheria, and that thus human 

 epidemics may be originated. In cases where this has been 

 suspected, a pustular ulcerative condition in the teats has been 

 described, but in neither disease is there definite evidence that 

 such changes are due to the causal virus. In the case of scarlet 

 fever, the evidence for this statement is indirect as the nature of 

 the virus is unknown. In diphtheria, virulent bacilli have been 

 isolated from such lesions by Dean and others, but the facts 

 rather point to a pustular eruption of other origin having been 

 secondarily infected by the bacilli from human contacts. 



Apart from diseased conditions of the cow itself, milk may 

 be a disseminating agent from being infected through being 

 handled by those suffering from disease. The two diseases most 

 commonly thus spread are diphtheria and typhoid fever. In 

 the former case the bacilli have been actually isolated from the 

 milk. With typhoid fever the chief danger lies in the milk 

 being contaminated by a "carrier" (see Chapter XV.). Further, 



