SENSITIZERS FOR THE TUBERCULE BACILLUS. 463 



of either human or avian bacilli. In other words, the serum ob- 

 tained following an injection of avian bacilli does not give a means 

 of distinguishing the two races of tubercle bacillus. 



If guinea-pigs are given injections of a mixture of human tubercle 

 bacilli, killed by heating to 70 degrees, and sensitizing serum, fol- 

 lowed at the end of 2 weeks by another similar mixture con- 

 taining simply dried bacilli, we find that the animals have become 

 more resistant than controls to the living human tubercle bacillus. 

 Such treated animals, on receiving an injection of this organism, 

 survive considerably longer than do the controls, but when killed 

 about 3 months after injection, their organs are found filled 

 with tubercles, notwithstanding; in other words, the rapidity of 

 the disease is simply checked. The serum of such animals tested 

 at this period shows the presence" of a sensitizer. The sensitizing 

 property, then, although not quite useless, is incapable of prevent- 

 ing the evolution of the disease. Guinea-pigs that have been 

 treated simply with injections of human bacilli killed by heating 

 to 70 degrees, followed by dried bacilli, also acquire a sensitizing 

 property in their serum, but, as we have already known for some 

 time, their resistance to the living bacillus has not been remark- 

 ably increased. 



