MECHANISM OF INFECTION IN TUBERCULOSIS 349 



which the tonsils showed no signs of tuberculosis to the naked 

 eye, there was some microscopic evidence of tuberculosis. 



Apparently it would seem that a strong case for tuberculous 

 infection through the agency of milk is hereby established. It 

 is not without significance, however, that though tuberculosis 

 is common during the first years of life, particularly in the 

 second and third years, advanced infection of glands in the 

 neck is far more rare than at later periods and is seldom present 

 unassociated with a much older lesion in the glands of the 

 respiratory tract. 



Babies fed at breast or from the bottle must suck to obtain 

 their food and of necessity naturally breathe through their noses. 

 On the other hand, older children, from two years upwards, 

 soon become mouth-breathers. 



Whereas air drawn in through the nose never comes into 

 contact with the tonsils, the reverse is the case in mouth- 

 breathers, who for this reason are constantly subject to tonsillar 

 infections. 



We are confronted therefore with the fact that, at the age 

 when nose-breathing and milk-feeding are associated, infection 

 of the glands in the neck is undoubtedly rare, whilst later on, 

 when mouth-breathing is more frequent and milk no longer the 

 only diet, the glands in the neck are frequently invaded by 

 tubercle. 



The evidence of tuberculosis in swine may be referred to 

 here as appropriate in this connexion. It is universally 

 admitted that swine are infected owing to their promiscuous 

 habits of feeding. They suffer from tuberculous ulceration of 

 the intestine and its associated lymphatic glands. They occa- 

 sionally show tuberculous tonsillitis and disease of the sub- 

 maxillary glands together with those which lie behind the 

 pharynx and in the upper part of the neck. A form of the 

 disease peculiar to swine is a tuberculosis spreading from 

 pharynx to mid-ear upwards into the brain. Clearly, therefore, 

 in cases in which the infection is definitely due to food, the 

 tonsil is frequently implicated. 



On the other hand, dogs and horses, the associates of adult 

 man, who presumably derive tubercle bacilli from inhaled dust 

 and the spray distributed by tuberculous stable-hands in cough- 

 ing, show a large preponderance of infection of the respiratory 

 tract — in the case of dogs 75 per cent. 



