OLD TUBERCULIN 305 



bacilli be virulent or non-virulent, or whether they be 

 of human or of mammalian origin. The cultures, bacilli 

 and all, are heated at 115 C. in the autoclave for half an 

 hour, then concentrated over a water-bath to about one 

 tenth of their volume, and finally are filtered through 

 porous porcelain ; the resulting fluid is thick, owing to 

 the concentration of the glycerin by the evaporation, is 

 of a dark amber colour, and possesses a curious charac- 



FIG. 38. Flask for growing tuberculin. 



teristic smell. The large proportion of glycerin preserves 

 the fluid, which keeps indefinitely in a cool dark place. 



This old tuberculin possesses remarkable properties. 

 Relatively large amounts (O1-O5 c.c.) may be injected 

 into a healthy animal or individual without effect, but 

 in a tuberculous one a minute dose, O001 c.c. or less, gives 

 rise to a marked reaction elevation of temperature with 

 constitutional disturbance more or less severe, and swelling 

 and tumefaction of tuberculous lesions (glands, ulcers, 

 etc.), and this reaction is made use of for diagnostic pur- 

 poses (see p. 330). By cautiously increasing the amount 

 a toleration is gradually induced, so that considerable 

 doses cause little or no disturbance. Injections of tuber- 

 culin tend to produce marked changes in the tuberculous 

 parts, leading to necrosis and exfoliation, with subsequent 

 healthy reaction and repair. This is especially seen in 

 cases of lupus ; by continued injections a marvellous 



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