578 INFECTION AND IMMUNITY. 



terial cell (Koch). This substance is 100 times 

 as toxic for tuberculous animals as for healthy and 

 causes an increase in the eosinophiles of the blood. 

 In addition to the fever-producing substance, 

 Maragliano and others recognize as a constituent 

 of the bacillus a heat susceptible "toxalbumin" 

 (destroyed at 100 C.) which reduces temperature. 

 Hammerschlag speaks of a toxin which in animals 

 causes fatal convulsions. The toxic products of the 

 tubercle bacillus show their greatest toxicity when 

 injected into the brain, and this method of injec- 

 tion has been suggested for the standardization of 

 tuberculin. 



Tuberculin. Of the toxic .preparations of the bacillus the 

 greatest interest attaches to tuberculin which 

 Koch, in 1891, announced as an agent which could 

 be used for the specific diagnosis of tuberculosis 

 and which, when properly administered, had cer- 

 tain curative effects. Its preparation is simple. 

 Cultures are allowed to grow for four weeks in 

 peptone bouillon which contains 5 per cent, of 

 glycerin. At the end of this time the organisms 

 are killed by exposure to a temperature of 100 C. 

 for one hour (Marx). The fluid is reduced to one- 

 tenth its original volume by evaporation under a 

 vacuum at a low temperature and the bacterial 

 cells are eventually removed by filtration. The 

 percentage of glycerin which is present in the final 

 preparation acts as a preservative, but 0.5 per 

 cent, carbolic acid may be added in addition. The 

 active substance in tuberculin may be precipitated 

 by 66 per cent, alcohol; its chemical nature re- 

 mains unknown. - 



In addition to the "old tuberculin," which has 

 just been described, Koch has made several other 



