380 Tuberculosis 



liberation of their essential toxic and immunizing con- 

 stituents. 



Koch therefore endeavored to bring about artificial con- 

 ditions advantageous to the absorption of the bacilli, and 

 for the purpose tried the solvent action of diluted mineral 

 acids and alkalies. The changes thus brought about facili- 

 tated absorption, but the absorption of bacilli in this chemi- 

 cally altered condition was not followed by immunity, prob- 

 ably because the chemic composition of tubercle toxin (or 

 whatever one may name the poisonous product of the 

 bacillus) was altered by the reagents. 



Tuberculin, with which Koch performed many experi- 

 ments, was found to produce immunity only against tuber- 

 culin, not against bacillary infection. 



Pursuing the idea of fragmenting the bacilli, or treating 

 them chemically to increase their solubility, Koch found 

 that a 10 per cent, sodium hydrate solution yielded an 

 alkaline extract of the bacillus, which, when injected into 

 animals, produced effects similar to those following the 

 administration of tuberculin, except that they were more 

 brief in duration and more constant in result ; but the dis- 

 advantage of abscess-formation following the injections re- 

 mained. The fluid, when filtered, possessed the properties 

 of tuberculin. 



Mechanical fragmentation of bacilli had been employed 

 by Klebs in his studies of antiphthisin and tuberculocidin, 

 and Koch now used it with advantage. He pulverized living, 

 virulent, but perfectly dry bacilli in an agate mortar, in 

 order to liberate the toxic substance from its protecting 

 envelop of fatty acid, triturating only very small quantities 

 of the bacteria at a time. 



Having thus reduced the bacilli to fragments, he removed 

 them from the mortar, placed them in distilled water, 

 washed them, and collected them by cent rifugat ion, as 

 a muddy residuum at the bottom of an opalescent, clear 

 fluid. For convenience he named the clear fluid TO; 

 the sediment, TR. TO was found to contain tuberculin. 

 In order to separate the essential poison of the bacteria as 

 perfectly as possible from the irritating tuberculin, the TR 

 fragments were again dried perfectly, triturated once 

 more, re-collected in fresh distilled water, and recentrifu- 

 gated. After the second centrifugation microscopic examina- 

 tion showed that the bacillary fragments had not yet been 



