IMMUNITY IN TUBERCULOSIS 241 



of the difficulties of the method. The same difficulty has been en- 

 countered in the practical carrying out of this method of immunization 

 in cattle. Several series of guinea-pigs were inoculated with tubercle 

 bacilli as follows: (a) with dead bacilli, (b) with living bacilli from 

 cold-blooded animals, (c) with a culture of human bacilli cultivated 

 artificially for more than twenty years which produces on inoculation 

 no appreciable local lesions and never tends to generalize, and (d) 

 another human culture cultivated artificially for more than fourteen 

 years, which still causes in all the pigs slightly enlarged inguinal 

 glands near the site of inoculation, and occasionally brings about slight 

 caseation of the nodes with a tendency to partial generalization of the 

 virus. The dead bacilli and the bacilli from cold-blooded species gave 

 no protection; the second human culture, by reason of its greater in- 

 vasive properties, protects better than the first, which is almost devoid' 

 of power to grow in the animal body. In no case, however, was the 

 growth of the virulent bacilli wholly suppressed. 



In man the question of acquired immunity has been answered by 

 many authorities, as far as the main considerations go, in the negative. 

 A large number of well-observed facts demonstrates that a person who 

 has suffered from localized tuberculosis of the lymph glands — scrofula 

 so-called — or other form of local tuberculosis, can not count upon an 

 immunity from pulmonary tuberculosis. And yet it can, I think, be 

 shown by reference to statistics that in man there exists a refractory 

 condition which becomes increased after infection, since the number of 

 persons who have been the victims, at some period of their life, of a 

 tuberculous infection, is very large in comparison with the number who 

 die of this disease, or the even larger number who develop severe forms 

 of it. Hirsch gives the mortality of tuberculosis as compared with 

 deaths from all other causes as 3 :22, in other words, tuberculosis claims 

 as victims of death 1 in every 7 persons. This proportion does not, 

 however, express the morbidity from tuberculosis, which is. in reality, 

 far greater than these figures indicate. It is difficult to secure by vital 

 statistics reliable data of the incidence of tuberculosis ; but trustworthy 

 observations made at autopsies upon human beings indicate that as 

 many as 90 per cent, of persons, dying from all causes, have at some 

 period of their life been the victims of a tubercular infection. In far the 

 greater number of instances the disease remains fixed in the bronchial 

 or other lymphatic glands or the apex of the lungs and exerts no in- 

 jurious effect upon the organism as a whole. We may, therefore, fairly 

 conclude that the human organism possesses a strong inherent tendency 

 to overcome infection with the tubercle bacillus. So much can be safely 

 predicated. But whether the suppression of a local infection, such as 

 I have described, gives an increased capacity for overcoming subse- 

 quently invading tubercle bacilli remains for the present an open 



VOL. LXIX. — 16. 



