MECHANISM OF INFECTION IN TUBERCULOSIS "337 



high, by a somewhat questionable process of reasoning some 

 authorities have placed the blame upon the milk supply. 



Inasmuch as our ideas are inevitably the result of impres- 

 sions received, the result of this insistence has been that not 

 only the majority of the thinking community but many phy- 

 sicians and even the Local Government Board authorities them- 

 selves are persuaded that at least in the case of young children 

 milk is the prime source of tuberculous infection. 



Far more stringent regulations than those applied to milk 

 control the sale of meat for human food. Beasts showing any 

 evidence of tuberculosis and carcases in which tuberculous 

 lesions are present are rigorously condemned by the meat 

 inspectors. 



Milk being entirely derived from bovine sources in our 

 country and meat very largely so, investigators directed their 

 attention at an early date to such differences as exist between 

 tubercle bacilli occurring in the ox and in man. 



Distribution of Tuberculosis 



No disease is more universally prevalent throughout the 

 animal kingdom than tuberculosis. A similar disease occurs 

 in reptiles; birds also, especially in captivity, are prone to 

 tuberculous invasion and the avian bacillus has been found 

 to be possessed of definite characteristics ; in fact, all animals 

 are susceptible to tuberculosis and in the collection of the 

 Zoological Society, as well as in similar menageries all over 

 Europe, no disease is more prevalent nor more fatal. Bovines 

 seem specially susceptible to pulmonary and abdominal tuber- 

 culosis and sometimes suffer from tuberculous diseaseof the udder. 



Of the smaller mammals — mice, rats, guinea pigs, rabbits, 

 etc. — used in laboratories for inoculation experiments, the guinea 

 pig is very readily infected by tuberculous material. 



It is scarcely necessary to . refer to the great variation in 

 relative susceptibility to tuberculosis which is noticeable in the 

 different races of man. Europeans show a high degree of 

 natural and acquired immunity, whilst the liability to infection 

 of races which have no previous experience of the disease is 

 common knowledge. Thus the North American Indians are 

 said to have been decimated, indeed almost exterminated, by 

 tuberculosis ; the Sandwich Islanders afford another illustration 



