MECHANISM OF INFECTION IN TUBERCULOSIS 339 



The Mechanism of Infection 



Careful consideration of the mechanism of infection is clearly 

 of the first importance in view of the wide prevalence and heavy 

 mortality from tuberculosis. When such foods as milk and 

 meat are implicated as causes of the disease and not only the 

 health of the community but vast commercial interests are at 

 stake, the propriety of reviewing the evidence that milk and 

 meat are the carriers of infection is beyond question. 



The matter may well be approached by considering the 

 lesions of tuberculosis, as they occur in man at the various stages 

 of his existence, under the varying conditions of function and 

 environment which attend infancy, adolescence, maturity and 

 old age. 



Few generalisations are more remarkable than the freedom of 

 infants from disease other than nutritional disorders during 

 the first year of life. Marked as this immunity is in breast- 

 fed infants, it is equally striking in those brought up by hand. 



The suggestion has been advanced that by means of the 

 intimate apposition of foetal and maternal blood which attends 

 intra-uterine life, the growing embryo obtains from its mother 

 substances which serve to protect it from the attacks of patho- 

 genic micro-organisms in the early months of its existence. 

 These substances, it may be, are of the nature of anti-bodies, 

 which are preformed by the mother in response to infections 

 which she from time to time incurs ; or, perhaps, during the 

 nine months of its foetal existence, the child obtains doses of 

 the commonly occurring bacterial poisons by diffusion from the 

 maternal blood. 



In response to the stimulation of these toxins, the child 

 prepares its own anti-bodies, the mother having, in the nature 

 of the case, previously tempered the virulence of the infection 

 below the minimum harmful dose by the exercise of her own 

 protective mechanisms. Even in uiero, cases are recorded of 

 foetal infection associated with advanced maternal tuberculosis 

 but these are extremely rare. 



I would take this opportunity, however, of insisting that so 

 far as the acute infectious diseases of childhood are concerned, 

 milk is not a source of infection in infants, since in children up 

 to the age of one year they scarcely if ever occur. Furthermore 

 the epidemic diseases carried by milk are few. The infection of 



