SOURCES OF HUMAN TUBERCULOSIS. 229 



that there was ulceration of the intestine in 43. It is 

 especially in children that this mode of infection occurs, as 

 in the adult ulceration of the intestine is rare as a primary 

 affection, though it is common in phthisical patients as the 

 result of infection by the bacilli in the sputum which has 

 been swallowed. There is less risk of infection by means 

 of the flesh of tubercular animals, for, as stated by the 

 recent Tuberculosis Commission, in the first place, tuber- 

 culosis of the muscles of oxen being very rare, there is 

 little chance of the bacilli being present in the flesh unless 

 the surface has been smeared with the juice of the tuber- 

 cular organs, as in the process of cutting up the parts ; 

 and in the second place, even when present they will be 

 destroyed if the meat is thoroughly cooked. 



We may state, therefore, that the two great modes of 

 infection are by inhalation and by ingestion, of tubercle 

 bacilli. By the former method the tubercle bacilli will in 

 most cases be derived from the human subject ; in the 

 latter, probably from tubercular cows, though contamina- 

 tion of food by tubercular material from the human subject 

 may also occur. It is quite possible that bacilli from these 

 two sources may be of somewhat different virulence towards 

 the human subject, but at present we have not the means 

 of speaking definitely on this point. Both in inhalation 

 and in ingestion, tubercle bacilli may lodge about the 

 pharynx and thus come to infect the pharyngeal lymphoid 

 tissue, tonsils, etc., tubercular lesions of these parts being 

 much more frequent than was formerly supposed. Thence 

 the cervical lymphatic glands may become infected, and 

 afterwards other groups of glands, bones, or joints, and 

 internal organs. 



Koch's Tuberculin. We have seen that the pathology 

 of tuberculosis indicates that the tubercle bacillus can act on 

 tissues with which it is not immediately in contact, and there- 

 fore it is natural to ask whether it, like other organisms, pro- 

 duces definite toxic bodies. What knowledge we have of 

 the latter is secondary to the bringing forward by Koch 

 of a substance he called "tuberculin," which he intro- 



