vii TUBERCULOSIS OF THE COW 151 



testinal tuberculosis is with us a very rare occurrence. The only 

 exception to this is at Kiel, where Heller has found 3 7 '8 per cent 

 of primary intestinal tuberculosis at necropsies of tuberculous 

 children. 



The value of such statistics in part depends upon the 

 possibility of infection by ingestion without involvement of the 

 intestine or even the mesenteric glands. There is a consider- 

 able body of evidence showing that this may take place. 



Behring, in 1903, advanced a theory of phthisis causation 

 to the effect that infection takes place in the early years of 

 life, usually through cows' milk, the bacilli being absorbed 

 through the intestine before the powers of resistance of the 

 intestine are fully developed. The bacilli remain latent until 

 the resistance of the individual is impaired, when the disease 

 then becomes active. This view has not met with wide 

 acceptance, and there are many facts which are against it. 



During recent years extended investigation has been carried 

 out to study and determine the paths of infection in tuber- 

 culosis. Careful experiments have proved conclusively that 

 ingested tubercle bacilli may pass through the intestinal 

 mucous membrane without causing any lesion. Griffith, for 

 example, working for the Koyal Commission on Tuberculosis, 

 found that tubercle bacilli would pass through the intact 

 mucous membrane of the dog's intestine, but not in large 

 numbers or with any certainty. The evidence that they may 

 pass through the mesenteric glands in addition without setting 

 up morbid changes is, however, less firmly attested, and the 

 existing facts cannot be accepted as settling the question. 



The matter is too controversial to be dealt with in detail 

 in the space which is available, and involves the discussion of 

 the whole question of the inhalation and ingestion theories of 

 the paths of entry. After a careful review of the subject, 

 Cobbett l gives his opinion that 



. . . while I believe that phthisis is commonly caused by the 

 inhalation of tubercle bacilli, I do not deny that many cases of 

 tuberculosis, especially in children, are caused by bacilli which gain 

 entrance through the mucous membrane of the intestine. In such 

 cases, I believe, there are usually lesions in the mesenteric glands, 

 and not rarely in the gut itself. On the question whether tubercle 



1 Journ. of Pathology and Bacteriology, 1910, xiv. p. 563. 



