Toxic Products 



739 



From the "crude" or original tuberculin Koch prepared a purified or 

 "refined" tuberculin by adding one and one-half volumes of absolute 

 alcohol, stirring thoroughly, and standing aside for twenty-four hours. 

 At the end of this time a flocculent deposit will be seen at the bottom of 

 the vessel. The supernatant fluid is carefully decanted and an equal 

 volume of 60 per cent, alcohol poured into the vessel for the purpose of 

 washing the precipitate, which is again permitted to settle, the fluid 

 decanted, and the washing thus repeated several times, after which it is 



Fig. 246. Massive culture of the tubercle bacillus upon the surface of 

 glycerin-bouillon, used in the manufacture of tuberculin. 



finally washed in absolute alcohol and dried in a vacuum exsiccator. 

 The white powder thus prepared is fatal to tuberculous guinea-pigs in 

 doses of 2 to 10 mg. It is soluble in water and glycerin and gives the pro- 

 tein reactions. The tuberculin as Koch prepared it is now known as 

 "concentrated" or "Koch's tuberculin," to differentiate it from the 

 "diluted tuberculin" sometimes sold in the shops, which is the same 

 thing so diluted with i per cent, aqueous carbolic acid solution that i c.c. 

 equals a dose. The dose of the concentrated tuberculin is 0.4 to 0.5 c.c. ; 

 that of the diluted tuberculin, i c.c. 



