SPECIFIC BACTERUL REACTIONS 171 



Sjoengler's Perlsucht Tuberculin {'' P. T. O/') .— 

 Perlsucht signifies *' pearl disease " in cattle, that is, 

 true bovine tuberculosis. Spengler believed that a 

 tuberculin prepared from this strain of the tubercle 

 bacillus would prove most efficacious in the treatment 

 of human tuberculosis, and indeed such was the case in 

 his experience. The method of preparation of 

 Spengler's tuberculin is precisely identical with that 

 of Koch's old tuberculin. 



Dixon's Tuberculin. — This product is a saline ex- 

 tract of living tubercle bacilli minus their fat. Six to 

 eight weeks old cultures from four per cent, glycerin 

 veal broth are removed and collected on hard filter 

 paper. Equal quantities, by weight, of human and 

 bovine types of bacilli are placed between sterile filter 

 paper and dried in a thermostat for twenty-four to 

 forty-eight hours. The dried bacteria are then treated 

 in an excess of ether until all water and glycerin are 

 removed. Further extraction of the fat with fresh 

 ether is done and the same is removed from the bottom 

 of the vessel by a Pasteur pipette. After the bacillary 

 mass has been thoroughly dried and freed from ether, 

 it is ground in an agate mortar and suspended in nor- 

 mal saline in the proportion of parts one to five. The 

 suspension is then shaken for eight to ten hours, after 

 which it is allowed to stand at room temperature for 

 several days. Finally it is filtered until the filtrate is 



