318 



VETERINARY BACTERIOLOGY 



tion of their products. As will be noted later, tuberculin is not 

 only of therapeutic significance, but of great diagnostic value. 

 Many types have been prepared by various workers. Some of 

 the more important will be described before a discussion of their 

 use in immunization and in diagnosis is undertaken. 



Fig. 131. Tuberculin flask, showing the growth of Bacillus tuberculosis 



(McFarland). 



Koch's Old Tuberculin (Alt Tuberculin) .Flat-bottomed 

 flasks containing 4 per cent, glycerin broth to a depth of 2 to 3 cm. 

 are inoculated with B. tuberculosis. The inoculated material is 

 carefully placed on the glass at the surface of the liquid in order 

 that it may spread out at once as a film over the surface. Unless 

 the organism is at the surface, little or no growth will occur. In 



