EXTERCOMMUXTC ABILITY OF TUBERCULOSIS. 
813 
extent tuberculosis in man depends on these sources of infection. In 
considering this question, with the object of arriving at a reasonable 
conclusion on the point, a number of circumstances have to be 
reflected on. It will have been noted that in the cases of trans- 
mission from cows to pigs which I have just reported, the infection 
occurred by ingestion, and the predominant lesions were in the 
intestines or mesenteric lympathic glands. In those cases in which 
lesions existed in other organs (with the exception of the tonsilar and 
pharyngeal lesions) they were evidently secondary to mesenteric 
invasion. This is a point of paramount interest when it is remem- 
bered that intestinal or mesenteric tuberculosis as a primary affection 
in the human being is almost wholly confined to children under five 
years old, whose sole aliment during a considerable portion of their 
existence has been milk. The deduction to be drawn from the analogy 
is that the method of infection in infants is by ingestion. I am glad 
that this phase of the subject has been so authoritatively ventilated 
recently by Dr. Sims-Wooahead, a pathologist who has always been to 
the front in the investigation of the relationship of human and animal 
diseases. At the International Hygienic Congress, in London, he 
reported that of 127 cases of tuberculosis in children there were 100 cases 
in the mesenteric glands, apparently primary — i,e*, 79 per cent. In only 
twenty of these 100 cases had abdominal tuberculosis been diagnosed. 
Again, in an address delivered before the North London Mcdico- 
Clvirurgical Society, 18th October, 1894, he says: “It cannot be too 
strongly insisted upon— and l am sure that those of you who have made 
any considerable number of post-mortem examinations of the bodies of 
tuberculous patients who have succumbed at various periods of life will 
agree with me in this — that the affection of the lung often appears to be 
(although the ultimate cause of death) merely a secondary affection. 
I have seen in case after case of children, and in animals fed on 
tuberculous material, the lungs markedly affected, but in a large pro- 
portion of these cases it lias been possible to trace the course of 
invasion back from a caseous or old calcareous mesenteric gland 
through the chain of retroperitoneal glands, up through the diaphragm 
to the posterior mediastinal and bronchial glands, and so on to the 
lung. I have not seen this in a few cases only, but in dozens of 
children, in a few adults, and in many animals. . . . The import- 
ance of the hearing of these facts is evident when it is considered that 
in all probability tuberculosis of the alimentary tract and of the 
mesenteric glands can be brought about only by the introduction of 
tuberculous material, usually milk in the case of children.” 
Connecting these statements with my own experience in the 
disease in pigs, I would point out, in order that the importance of the 
cases I have recorded should not be minimised, that of all domestic 
animals the pig most nearly approaches the human being in anatomical 
and histological structure, and in pathological processes— i.e,, the 
reaction to pathogenic agents. They are alike omnivorous. The 
Btomach, intestines, and epidermal appendages are remarkably alike. 
The quantity and distribution or lymphoid tissue in the alimentary 
canal of the pig (tonsils, Peyer’s patches, &c.) are very similar to those 
in man. The pig is the only animal in which there is a tendency to 
intestinal ulceration similar in character and situation to that seen in 
man in typhoid fever. 
