248 TUBERCULOSIS. 



boiling or by the addition of a 5 per cent solution of 

 carbolic acid. 



Another great source of infection is the milk of cows 

 affected with tuberculosis of the udder. In such cases the 

 presence of tubercle bacilli in the milk can usually be 

 readily detected by centrifugalising it, and then examining 

 the deposit microscopically, or by inoculating an animal 

 with it. As pointed out by Woodhead and others, the 

 milk from cows thus affected is probably the great source 

 of tabes mesenterica, which is so common in young sub- 

 jects. In these cases there may be tubercular ulceration 

 of the intestine, or it may be absent. Woodhead found 

 that out of 127 cases of tuberculosis in children, the 

 mesenteric glands showed tubercular affection in 100, and 

 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 probable 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 



