MECHANISM OF INFECTION IN TUBERCULOSIS 345 



end of his illness, when his resistance failed, these bacilli 

 effected a settlement in the intestinal wall and caused ulceration. 



Sometimes but far less commonly it happens that the 

 primary focus from which tubercle bacilli find their way into 

 the blood is situate in a mesenteric gland, the resting-place of 

 tubercle bacilli which have reached it from the intestines. In 

 these cases, the distribution of the bacilli in the miliary tuber- 

 culosis which ensues still remains identical with that in the 

 case described — which originated in glands connected with the 

 respiratory system — and is amenable to a similar explanation. 



Pulmonary tuberculosis or Phthisis Pulmonum is by no 

 means unknown even in very young children. Starting some- 

 times from a bronchial lymph gland, infected as I have 

 described, the bacilli attack the wall of an adjacent large air 

 tube and tubercle bacilli are sucked by the movements of 

 breathing to all parts of the lung on the affected side, there 

 giving rise to a tuberculous broncho-pneumonia. 



It may happen too that tuberculosis will attack the lungs of a 

 child recovering from an attack of measles or of whooping-cough. 



During adolescence — the years from twelve to eighteen — 

 attacks of tuberculosis are less frequent or severe. It would 

 seem that the weakly ones who are either born naturally 

 susceptible or are unduly subjected to infection from tubercle 

 bacilli have succumbed and that the survivors are relatively a 

 hardier race. 



At this period of life the young human being becomes to 

 a large extent independent of its parents' efforts. Learning, 

 as experience grows, to safeguard himself from unnecessary 

 fatigue, delighting in a life spent in the open air, his natural 

 liking for good food in abundance is his surest defence against 

 an organism which flourishes best on bodies vitiated by star- 

 vation. At no time is he so keenly appreciative of all in his 

 surroundings that is conducive to enjoyment nor will he, at any 

 other time, experience such freedom from the cares of life and the 

 overwork which beset later years. Such factors as these are 

 valid means of defence against an organism certainly as old 

 as civilised humanity, which has been evolved on lines parallel 

 with the evolution of man himself, at one time successful in the 

 struggle, finding suitable soil in races before inexperienced, at 

 another spreading but slowly amongst peoples long accustomed 

 to its attacks. 



