CHAPTER XXVI 



HYPERSENSTTIVENESS DUE TO INFECTION 



Allerg-y in Tuberculosis 



Tuberculosis and Tuberculin Hypersensitiveness. — In 1891, 

 Koch made the remarkable discovery that active tuberculosis in 

 guinea pigs renders them extremely sensitive to extracts of old 

 autolyzed glycerin broth cultures of the tubercle bacillus. He 

 concluded that the active substance to which they become sen- 

 sitive is a protein fraction of the bacterial cell and accordingly 

 named it "tuberculin." 



Tuberculin OT, BE, and TR. — In his original work, Koch em- 

 ])loyed a filtrate of a glycerin broth cultui-e of the tubercle bacil- 

 lus that had been incubated at 37° C. for six or eight weeks, 

 sterilized and concentrated to one-tenth its volume. In an attempt 

 to obtain a better yield of the specific active substance, Koch pre- 

 pared a bacillary emulsion of the tubercle l)acillus in glycerol and 

 water and also a combined extract of finely pulverized bacteria. 

 The former tuberculin he designated as BE and the latter as TR. 

 It is interesting to note that of all Kocli 's preparations his original 

 or old tuberculin, OT, is the one that lias been most generally ac- 

 cepted. It is used quite extensively at the present time in the diag- 

 nosis and to a limited extent in the treatment of tuberculosis. 



Objections to OT. — Certain objections to Koch's old tuberculin 

 have been made by numerous investigators. It has been pointed 

 out (1) that the meat broth employed as a culture medium con- 

 tains protein derivatives and perhaps protein from the peptone 

 and meat used in its preparation; (2) the old glycerin broth 

 culture contains products of bacterial metabolism and bacterial 

 autolysis other than the active tuberculin fraction. 



Long's Synthetic INIedium. — The first objection has been met 

 by growing the tu])ercle bacillus in a synthetic medium. While a 

 great many methods and formulae for preparing a medium of 

 known chemical constitution have been used, the synthetic me- 

 dium devised by Long is regarded in America as the first satis- 

 factory one. It contains glycerol, asparagine, acid potassium 



504 



