ACTION OF DEAD TUBERCLE BACILLI 257 



inoculating them with dust collected from the walls of a con- 

 sumptive ward. Tubercle bacilli are also discharged in consider- 

 able quantities in the urine in tubercular disease of the urinary 

 tract, and also by the bowel when there is tubercular ulceration ; 

 but, so far as the human subject is concerned, the great means 

 of disseminating the bacilli in the outer world is dried phthisical 

 sputum, and the source of danger from this means can scarcely 

 be over-estimated. Every phthisical patient ought to be looked 

 upon as a fruitful source of infection to those around, and should 

 only expectorate on to pieces of rag which are afterwards to be 

 burnt, or into special receptacles which are to be then sterilised 

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

 carbolic acid. 



Another great source of infection is in all probability 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 subjects. 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 infection, 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, in the first place, tuberculosis 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 

 tubercular 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 inhaled tubercle bacilli may also be swallowed and 

 contamination of food by tubercular material from the human 

 subject may occur. Alike when inhaled and when ingested, 

 tubercle bacilli may lodge about the pharynx and thus come to 

 17 



