376 Tuberculosis 



at 37 C. In the course of some days a slight surface growth 

 becomes apparent about the edges of the floating bacillary 

 mass, which in the course of time develops into a firm, 

 coarsely granular, wrinkled pellicle. At the end of some 

 weeks development ceases and the pellicle sinks, a new 

 growth sometimes occurring from floating scraps of the 

 original growth. 



Some bacteriologists prefer to use small Erlenmeyer flasks 

 for the purpose, but large flasks such as are shown in the 

 illustration, and which may contain from 500 c.c. to i liter, 

 are more convenient. The contents of a number of flasks 

 of well-grown cultures are poured into a large porcelain 

 evaporating dish, concentrated over a water-bath to one- 

 tenth their volume, and filtered through a Pasteur-Cham- 

 berland filter. This is crude tuberculin. 



When doses of a fraction of a cubic centimeter of crude 

 tuberculin are injected into tuberculous animals, an in- 

 flammatory and febrile reaction occurs. Superficial tuber- 

 culous lesions (lupus) sometimes ulcerate and slough away. 

 The febrile reaction is sufficiently characteristic to be of 

 diagnostic value, though tuberculin can only be used with 

 perfect safety as a diagnostic agent upon the lower animals. 



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 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 2-10 mg. It is soluble in water and glycerin 

 and gives the proteid 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 tubercu- 

 lin is 0.4-0.5 c.c. ; that of the diluted tuberculin, i c.c. 



Tuberculin Test for Tuberculosis of Cattle. The febrile 



