284 TUBERCULOSIS 



The Specific Reactions of Tubercle Bacillus. The tubercle 

 bacillus belongs to the group of organisms which do not secrete 

 soluble toxins into the media in which they are growing. It 

 shares with other members of the group the capacity to induce 

 serious changes in the metabolism of an animal. As, in other 

 similar cases, we are in the dark as to how these changes come 

 about, and thus can only summarise the chief effects which, by 

 present methods, can be detected as occurring in the bodies of 

 infected animals. These effects which, it may be remarked, are 

 of value in the diagnosis of tubercular affections, consist on the 

 one hand (a) of certain phenomena of supersensitiveness, and on 

 the other (6) of certain changes in the blood serum of tubercular 

 patients resulting from reactions of immunity. The former are 

 seen when the bacilli or substances artificially derived from their 

 bodies are introduced into the tissues of those suffering from 

 tuberculosis, and were first demonstrated by Koch in his work 

 on tuberculin. In recent times, examples of similar effects are 

 the ophthalmic reaction of Calmette and the cutaneous reaction 

 of von Pirquet. The changes in the blood serum of infected 

 persons depend on the presence of anti-substances in the blood. 

 These may be of the nature of (a) immune bodies which lead to 

 fixation of complement, and (b) precipitins, (c) agglutinins, (d) 

 opsonins. These may now be severally discussed in detail. 



(1) Phenomena of Supersensitiveness. (a) Koctis Old Tuber- 

 culin. Koch (1890-1) stated that if in a guinea-pig suffering 

 from the effects of a subcutaneous inoculation with tubercle 

 bacilli, a second subcutaneous inoculation of tubercle bacilli was 

 practised in another part of the body, superficial ulceration 

 occurred in the primary tubercular nodule, the wound healed, 

 and the animal did not succumb to tuberculosis. This reaction 

 was further studied by means of tuberculin, which consisted of 

 a concentrated glycerin bouillon culture of tubercle in which the 

 bacilli had been killed by heat. Its essential components pro- 

 bably were the dead and often macerated bacilli and the 

 substances indestructible by boiling which existed in these 

 bacilli, or which were formed during their growth. The in- 

 jection of '25 c.c. of tuberculin into a healthy man causes, in 

 from three to four hours, malaise, tendency to cough, laboured 

 breathing, and moderate pyrexia ; all of which pass off in 

 twenty-four hours. The subcutaneous injection, however, of 

 "01 c.c. into a tubercular person gives rise to similar symptoms 

 (now known as the tuberculin reaction), but in a much more 

 aggravated form, and in addition there occurs around any 

 tubercular focus great inflammatory reaction, resulting in necrosis 



