From what has been said in the Introduction, on the importance of the epithelium in protecting the health of the entire organism, the question naturally arises whether the mucous membrane of the intes tine, which is so often injured by the action of cows milk and therefore weakened, does not frequently allow bacteria to enter the internal organs, where they may develop and by their action produce further harm. That it does seems probable from the investigations of Czerny and Moser.
Tuberculosis.—The weakness of the intestine offers during the nursing period of a baby a possible cause for the appearance of one of the greatest of human scourges, tuberculosis. As Behring has expressed it, tuberculosis in the majority of cases, although it appears in late life, is dependent on the fact that tubercle bacilli at some time in earlier life have passed through the delicate wall of the intestine. In the in testine they have either produced a tuberculous lesion at once, or, lying dormant, have awaited a chance to reappear in later years. The intestinal wall of the nursing infant is asserted by Behring, from the experiments of Disse, to he more pervious to tubercle bacilli than is that of the adult. Disse is said to have proved, in the newly-born individuals of different, species, that the mucous layer which lies on the epithelium layer of the mu eons membrane, and which is unbroken in the adult, in the newborn is sieve-like. These Openings may make it possible for the tubercle bacilli to pass through, and so in another way may explain the early origin of tuberculosis. It is by no means certain that these conditions are as simple as they seem. In the first place, the findings of Disse have not been proved by others. In the second place, no one has ever proved that the mucous layer is the chief protecting element of the epithelium.
Those who support the theory that tuberculosis is transmitted through the air, point to the following fact as strong evidence. The greatest changes following an infection of certain bacteria, as well as the tubercle bacilli themselves, are found in the glands of that region in which the infection takes place. Authors who have been studying the frequency of tuberculous changes in the definite groups of lymph-nodes, find that the bronchial nodes in the majority of eases arc the ones chiefly affected, showing tuberculous changes of pronounced caseation. This fact ‘volild seem to show that the tubercle bacilli in all probability have passed through the mucous mcnihratie of that part of the body (the respiratory tract) into the bronchial lymph-nodes. According to the
findings of Weleminsky, it is apparently proved that the bronchial lymph-nodes occupy quite a definite position in the topographical sys tem of the lymphatics. Ile maintains that they drain the lymph streams of the neck as well as those coining from the intestine. (In the other hand, Bartel has shown that the bronchial lymph-nodes are differen tiated front the others by their internal structure. The bacilli which pass the imperfect filtering system of the cervical and the intestinal nodes are stopped by the bronchial caseation of the bronchial nodes is explained by means of the combined streams of bacilli which have passed through the mucous membrane of the mouth, throat, and intestine. Bartel has also proven that the normal mucous membrane of the intestine, even in the adult, may be pervious to the tubercle bacilli.
While these facts support the possibility of tuberculous infection by the mouth, throat. and the mucous meinhrane of the irate: tine, the theories defending the idea of an air-infection, as the probable impor tant origin of tuberculosis, are also sound. Certainly the fact that the bronchial lymph-nodes on the right are so much oftener affected than those on the left, seems to us to offer good evidence for the importance of an air-infection. The right bronchus must allow a greater amount of dust and bacteria to enter the lung than does the left. Tit the first place, it has a greater cross-section than the left, and in the second it runs more nearly parallel with the trachea, the left leaving the trachea at a comparatively sharp angle. Still another argument, and one not well known, is the following: Tubercle bacilli when on the mucous mem brane of the bronchus are a greater danger to the organism than when on the mucous membrane of the intestine. While on the one hand it is a normal task and function for the mucous membrane of the intestine to digest and destroy bacteria, on the other. the presence of only a few bacteria is a very powerful aphysiological stimulus to the bronchial mucous membrane, which is normally accustomed to air well purified by the ciliated epithelium of the upper Thus it seems to us more plausible that an infection with tuberculosis takes place more frequently through the air, than by the intestine. This seems true to us even though children take in more bacilli by the digestive than by the respiratory tract.