238 POPULAR SCIENCE MONTHLY 



fowl-cholera and black-leg. In these cases the living attenuated micro- 

 organisms are employed. 



Neither lasting nor marked immunity in tuberculosis can be ob- 

 tained by the inoculation of cultures of tubercle bacilli killed by heat, 

 sunlight or other agency. Dead tubercle bacilli are poisonous and 

 bring out a striking reaction of the organism, but this reaction does not 

 confer immunity to subsequent inoculations of the living germ. It may 

 well be that the dead bacilli, especially if reduced to impalpable powder 

 so as to facilitate absorption, may after injection raise the powers of 

 resistance in the organic forces, although the height of the sustained 

 forces is not sufficient to enable the body to throw off completely the 

 living infecting organism. It is easy to prove that the animal organism 

 is modified by the development within it of the tubercle bacilli; and 

 merely disposing of dead bacilli increases its power of reaction against 

 a second injection of dead tubercle bacilli; the second action being 

 much more vigorous than the first. (Theobald Smith.) The experi- 

 ments of Koch which immediately preceded the discovery of tuberculin 

 clearly demonstrated that tuberculous guinea-pigs into which tubercle 

 bacilli are reintroduced subcutaneously react in a very especial manner. 

 An active inflammatory process develops about the site of second inocu- 

 lation which eventually brings about the expulsion of bacilli with the 

 exudations; a voluminous slough forms, which, when shed, carries 

 with it a large number of bacilli ; and this shedding is followed neither 

 by the formation of a permanent ulcer nor hypertrophy of the neigh- 

 boring glands, a regular result of the primary inoculation. The tuber- 

 cular organism reacts in the same manner to dead as to living bacilli ; 

 the tuberculous animal has acquired immunity against reinfection or 

 reintoxication by the tuberculous virus, which, however, in no way 

 prevents the first inoculation from becoming generalized and setting 

 up a tuberculosis of almost all the organs. 



If we attempt an interpretation of these phenomena we can con- 

 clude that the organism, once it is poisoned with tubercle virus, becomes 

 supersensitive to the tubercle poison. This supersensitiveness is dis- 

 played in the manner of reaction upon re-inoculation of the tuberculous 

 organism to tuberculin and to dead and living tubercle bacilli. But the 

 organism poisoned with dead tubercle bacilli is not in reality tubercu- 

 lous ; it is, however, sensitized. In keeping with this distinction, it can 

 be said that while the tuberculous organism has acquired a degree of 

 immunity to reinfection, the organism merely poisoned with tubercle 

 bacilli has failed to develop this state of resistance. 



The experimental results, which I shall relate to you, upon which 

 are based our belief in the artificial production of immunity to tubercu- 

 losis, were all obtained by the use of living bacilli. It would, therefore, 

 seem as if in the course of their residence and development within the 



