ESMOND R. LONG 1029 



Much discussion has centered on the relation of this type of sensitization to ana- 

 phylaxis. Zinsser' has distinguished quite clearly between the two phenomena, and 

 his colleague Mueller/ and Laidlaw and Dudley ,5 independently have apparently 

 found the antigenic substance concerned in serum reactions and anaphylactic reac- 

 tions. This interesting substance is present in the bacilH themselves, and in the fil- 

 trates after culture of the bacilli, together with the active principle of the tuberculin 

 reaction. When separated from the latter it does not elicit the tuberculin reaction. It 

 is a carbohydrate gum, analogous to that olitained from pneumococci by Heidelberger 

 and Avery, known to be concerned in pneumococcus serum reactions. 



This separation of the substances responsible for the two types of reaction, both 

 of which can be obtained in tuberculous patients and artificially sensitized animals, 

 rules out the serum reactions as previously used as a means of standardizing tul:»er- 

 culin, as Okell, Parish, O'Brien, and their colleagues^ have clearly pointed out. 



The specificity of the tuberculin reaction, high if not absolute, makes the tuber- 

 culin test valuable in the diagnosis of tuberculous infection. This test is used most 

 extensively and reliably in the diagnosis of tuberculosis in cattle. Intracutaneous 

 injection in the caudal fold, subcutaneous injection in the neck and examination for 

 general reaction, and ophthalmic inoculation are the methods commonly used. 



In man the usefulness of the test as a means of recognizing active tuberculous dis- 

 ease is limited by the fact that the majority of adults have been infected with tuber- 

 culosis, and therefore sensitized to tuberculin, without developing what can be called 

 "clinical disease." Opie and McPhedran^ and others distinguish this latent from pro- 

 gressive tuberculosis, however, by using tuberculin in a careful, quantitative fashion. 



In the recognition of early tuberculosis of childhood tuberculin is a great aid, al- 

 though, obviously, the test detects with certainty here, too, only the incidence of in- 

 fection, which is likely to become latent without setting up clinical disease. Inasmuch 

 as infections in the earliest years of childhood seem more likely to result in clinical 

 disease than those of later years, the tuberculin test applied to young children is of 

 considerable prognostic significance. 



In epidemiological studies to determine the incidence of tuberculous infection in 

 large groups of people, tuberculin is invaluable. In fact, it is largely through the use 

 of tuberculin that we have been able to determine the time of life at which the original 

 tuberculous infections occur, to which the healed scars of tuberculosis almost invari- 

 ably found at necropsy in later years correspond. 



THE BASIS FOR TUBERCULIN TREATMENT OE TUBERCULOSIS 



The introduction of tuberculin in the treatment of tuberculosis will long be re- 

 membered as one of the most spectacular tragedies in the history of medicine. With 

 the medical profession and patients all over the world waiting trustfully on the man 

 whose lightest word was law in the field of tuberculosis, the discoverer of the tubercle 



' Zinsser, H.: /. Ex per. Med., 34, 495. 1921. 



2 Mueller, J. H.: ibid., 43, 9. 1926. 



3 Laidlaw, P. P., and Dudley, H. W.: Brit. J. E.xpcr. Path., 6, 197. 1925. 



" Okell, C. C, Parish, H. J., O'Brien, R. A., et al.: Lancet, p. 433. Feb. 27, 1926. 

 5 Opie, E. L., and McPhedran, F. M.: .iin. Rev. Tiiberc, 14,347. 1926. 



