296 TUBERCULOSIS 



character. Such disintegrated products (which may be looked 

 on as endotoxins), artificially prepared, were introduced by Koch 

 under the name of tuberculins, and the following are the chief 

 forms in use : 



(1) Koch's Old Tuberculin. This consists of a six-weeks'-old culture of 

 tubercle bacilli in 5 per cent, glycerin bouillon, evaporated down to a 

 tenth of its original volume, killed by heat, and filtered. It thus contains 

 the products of macerated bacilli, substances (not destroyed by heat) 

 formed from the medium during the growth of the organism or extracted 

 from the bacilli by the glycerin, and the remains of the medium. 



(2) Tuberculin- 0. Masses of living bacillary growth from surface 

 cultures on agar are dried in vacua, ground in an agate mill, treated 

 with distilled water and centrifugalised ; the supernatant clear fluid is the 

 tuberculin. As it gave no cloudiness on the addition of glycerin, Koch 

 concluded that it contained the glycerin soluble products present in the 

 "old tuberculin" and which were looked on as responsible for the necrotic 

 effects produced by the latter (vide infra). 



(3) Tuberculin-It. The deposit in the preparation of tuberculin-0 is 

 again ground up in distilled water, centrifugalised, and the clear fluid set 

 aside ; the process is again and again repeated with the residue until, 

 on centrifuging, none is left. The successive supernatant fluids are 

 mixed and concentrated, and constitute the tuberculin. As this fluid 

 gives a cloudiness with glycerin, Koch considered it contained the 

 glycerin insoluble constituents of the " old tuberculin/' 



(4) Koctis New Tuberculin (Bazillenemulsiori). A bacillary mass 

 is dried and ground in 50 per cent, glycerin in water till a clear fluid 

 results. This tuberculin is thus equivalent to a mixture of tuberculin-0 

 and tuberculin-R. 



(5) Tuberculin Bdraneck. This preparation is an extract of tubercle 

 bacilli with 1 per cent, phosphoric acid, the effect of which is supposed 

 to be to destroy some of the more harmful constituents. 



A number of other tuberculin preparations have been used, but the 

 above are the most important. 



The original tuberculin was introduced by Koch for the 

 treatment of local tuberculous infections. The supposed 

 rationale was that when the artificially produced toxins were 

 injected into the body their action, added to that of the bacilli 

 growing in the focus of infection, caused a sudden exacerbation 

 of the necrotic effect occurring around the bacilli, which resulted 

 in ulceration, whereby the living bacilli were thrown off. It 

 has been found that . the injection of the tuberculin directly 

 into the tubercular focus is often not followed by a tuberculin 

 reaction, and although there are other factors to be taken into 

 account this militates against the view that a local concentration 

 of toxin is a sufficient explanation of the phenomenon. The 

 tuberculins are now used for the purposes of diagnosis and to 

 originate immunisation. Their action is extremely complicated 

 and not yet clearly understood, and may be considered under the 



