190 PATHOGENIC BACTERIA. 



growth is apparent, which in the course of time develops 

 into a pretty firm pellicle and gradually subsides. At the 

 end of four or six weeks development ceases and the 

 pellicle sinks. The contents of a number of flasks are 

 then collected in an appropriate vessel and evaporated 

 over a water-bath to one-tenth their volume, then filtered 

 through a Pasteur-Chamberland filter. This is crude 

 tuberculin. 



When such a product is injected in doses of a fraction 

 of a cubic centimeter an inflammatory and febrile reac- 

 tion occurs. The inflammation sometimes causes super- 

 ficial tuberculous lesions (lupus) to ulcerate and slough 

 away, and for this reason is of some value in therapeutics, 

 although attended with the dangers mentioned above. 

 The fever is sufficiently characteristic to be of diagnostic 

 value, though the tuberculin can only be used as a diag- 

 nostic agent in practice upon animals. 



Numerous experimenters, prominent among whom are 

 Tizzoni, Cattani, Bernheim, and Paquin, have experi- 

 mented with the tubercle bacillus and tuberculin, hoping 

 that the principles of serum-therapy might be applicable 

 to the disease. Nothing positive has, however, been 

 achieved. The first-named observers claim to have im- 

 munized guinea-pigs in whose blood an antitoxin formed ; 

 the last-named thinks the serum of immunized horses 

 a specific for tuberculosis. The field of experimentation 

 is an inviting one, though the chronic course of the dis- 

 ease lessens the certainty with which the results can be 

 estimated. 



The Bacillus of Fowl-tuberculosis (Tuberculosis gal- 

 linarum}. The cases of tuberculosis which occasionally 

 occur spontaneously in chickens, parrots, ducks, and 

 other birds were originally attributed to the Bacillus 

 tuberculosis, but the recent works of Rivolta, Mafucci, 

 Cadio, Gilbert, Roget, and others have shown that, while 

 very similar in many respects to the Bacillus tuberculosis, 

 the organism found in the disease of birds has distinct 

 peculiarities which make it a different variety, if not a 



