372 A MANUAL OF BACTERIOLOGY 



concentration of the glycerin by the evaporation, is of a 

 dark amber colour, and possesses a curious characteristic 

 smell. The large proportion of glycerin preserves the 

 fluid, and it keeps indefinitely in a cool dark place. 



This old tuberculin possesses remarkable properties. 



Healthy guinea-pigs bear considerable injections with- 

 out harm ; but if they be tuberculous, if the disease 

 is advanced (eight to ten weeks after inoculation), 

 doses of 0-01 c.c. produce death ; if less advanced 

 (four to five weeks after inoculation) a larger dose, 0-2 

 to 0-3 c.c., is required ; but 0-5 c.c. always proves fatal. 



FIG. 41. Flask for growing tuberculin. 



The post-mortem appearances are congestion of the 

 lymphatics and viscera, and dark red spots, from mere 

 points to the size of a hemp-seed, on the liver and spleen. 

 These are due to enormous engorgement of the capillaries 

 in the immediate neighbourhood of tuberculous deposits, 

 actual extravasations of blood being rarely found. The 

 hsemorrhagic-like spots on the liver are almost patho- 

 gnomonic of death from tuberculin. 



Relatively large amounts of tuberculin (0-1-0-5 c.c.) 

 may be injected into a non-tuberculous animal or 

 individual without effect, but in a tuberculous one a 

 minute dose, 0-001 c.c. or less, gives rise to a marked 

 reaction elevation of temperature with constitutional 



