ESMOND R. LONG 1019 



tivity of all of the many varieties of tubercle bacillus preparations. Koch himself, in 

 his original article/ stated that the active principle appeared to be related to the pro- 

 teins. In his second investigation on tuberculin/ he endeavored "das wirksame Prin- 

 zip zu isolieren, urn es frei von anderen StofFen anwenden zu konnen," in the belief 

 that by thus concentrating it he might enhance the therapeutic action of tuberculin 

 and at the same time avoid certain disturbing non-specific manifestations in patients. 

 This work for its time was an exhaustive piece of chemical investigation. Seibert and 

 I have reviewed and analyzed his results elsewhere.^ Of various methods of precipi- 

 tation or concentration attempted, precipitation of glycerol extracts of tubercle bacil- 

 li with 60 per cent alcohol acted most favorably. This yielded a powder of high tuber- 

 culin potency, which he felt to be "vielleicht schon in Wirklichkeit das vollkommen 

 isolierte wirksame Prinzip des Tuberkulins." He called it "purified tuberculin." 

 It was a water-soluble substance, partially coagulable by heat, but stable as re- 

 gards activity in glycerol- water solution even at temperatures from 130° to 160° C. 

 It contained 14 per cent nitrogen and gave all of the common protein reactions. Acet- 

 ic acid precipitated it with some loss of activity. Alcohol precipitated it well only in 

 the presence of some sodium chloride. His preparations contained 16-20 per cent ash, 

 however, and he was forced to admit that this high ash content indicated considerable 

 admixture with impurities. In spite of his finding that material with tuberculin activ- 

 ity passed easily and rapidly through dialyzing membranes, he concluded that the 

 active substance belonged to the group of proteins. 



OTHER CONCEPTIONS 



Since Koch's time there has been only occasional dissent from the view that the 

 active principle "belongs to the group of proteins." Only one school, that of Hans 

 Much, implicates definite substances other than proteins or their derivatives. This 

 school, with views somewhat apart from the usual immunological concepts, holds 

 that tuberculin activity may be exhibited by lipoid as well as protein substances. 



Although most investigators have followed Koch in the belief that the active sub- 

 stance is related to protein, there have been marked differences of opinion as to the 

 type of protein substance involved. I have reviewed in detail elsewhere the various 

 contentions on this subject.'' The opinion has not infrequently been held that the 

 active substance is a protein derivative rather than a whole protein. Most of the de- 

 rivatives of protein recognized in the usual classifications of protein have been con- 

 sidered by one investigator or another to be responsible for tuberculin activity. One 

 of the earliest investigators, Ruppel,^ believed a nucleo-protein to be the active prin- 

 ciple. Matthes'' contended that a proteose was concerned. Lowenstein and Pick" 

 felt their evidence indicated that it was a polypeptide, and Jousset^ went so far as to 



' Koch, R.: op. cit., 17, loi. 1891. ^ Koch, R.: ibid., p. 1189. 1891. 



5 Long, E. R., and Seibert, F. B.: Tubercle, 8, iii. 1926. 



^ Wells, H. G., De Witt, Lydia, and Long, E. R. : The Chemistry of Tuberculosis. Baltimore, 1923. 



5 Ruppel, W. G.: Ztschr. f. phys. Chemie, 26, 218. 1899. 



^Matthes, M.: Deutsche Arch./, klin. Med., 54, 39. 1894. 



7 Lowenstein, E., and Pick, E.: Biochem. Ztschr., 31, 142. 1911. 



* Jousset, A.: Bull. Acad, de med., 71, 752. 1914. 



