482 THE TUBERCLE BACILLUS GROUP 
The Nature of Tuberculin.— Tuberculin^ appears to be a true 
product of the metabolism of the tubercle bacillus. It is thermostabile, 
non-dialyzable, insoluble in alcohol, gives no biuret reaction, and is pre- 
cipitated by certain alkaloidal precipitants as tannic acid, potassium 
mercuric iodide and mercuric chloride in acid solution. It is decom- 
posed by pepsin HCl and by trypsin in alkaline media. Proskauer 
and Beck,- and Lowenstein and Pick/ and others have shown that 
tuberculin is produced by the tubercle bacillus when this organism is 
grown in a protein-free medium. They suggest that it is probably a 
polypeptid. Long,* however, believes that the active principle of 
tuberculin is a protein. The protein nature of tuberculin has recently 
been shown by Florence Seibert through electrodialysis with special 
apparatus.^ 
Elementary Composition of Old Tuberculin Parts per 100 Dry Weight.^ 
Ash 16.6 -20.50 
Carbon 47.00-48.13 
Hydrogen 7.06- 7.55 
Nitrogen 14.45-14.73 
Sulphur 1.14-1.17 
Whether tuberculin contains a true toxin or an endotoxin,^ or a 
mixture of both toxin and endotoxin is not clearly settled. Pick 
believes it contains a true toxin secreted by the tubercle bacillus. 
Variants of Old Tuberculin.— A number of observers, impressed with 
the possibility that the reactive substances of tuberculin might be 
changed by heat, have attempted to produce tuberculin which has 
been unheated. 
(a) Bouillon Filtrate Denys (B. F.).^—This is unheated, uncon- 
centrated old tuberculin prepared as above and sterilized by passage 
through sterile porcelain filters. 
(6) Vacuum Titberculin.— The six weeks glycerin broth culture of 
the tubercle bacillus is concentrated to one-tenth its volume in vacuo 
and filtered. By so doing the adA'antages of concentration are obtained 
without the disadvantages of heating. 
The action of old tuberculin and its variants would suggest that it 
does not contain all the necessary elements for the establishment of 
true immunity, and this has led to the production of a series of new 
products, new tuberculins, which attempt to retain the more specific 
products of the tubercle bacillus. The principle involved is to grind 
1 The word "tuberculin" appears to have been used first by Pohl-Pincus (Deutsch. 
med. Wchnschr., 1884, 10, 108. 
■^ Ztschr. f. Hyg., 1894, 18, 128. ^ Biochem. Ztschr., 1911, 31, 142. 
* Am. Rev. Tuberc, 1926, 13, 448. 
■'• See Seibert and Hanke: .Jour. Biol. Chem., 192.S, 76, 5M5. 
* Quoted from Calmette: Loc. cit., p. 75. 
" Viquerat has made the statement that tuberculin is succinic acid. This is entirely 
unsupported by the observations of other investigators (Centralbl. f. Bakteriol., 1899, 
26, 293). 
» Denys: Le Bouillon filtro du Bacille de la Tuberculose, Louvain, 1905. 
