510 IMMUNOLOGY 



(1937). The skin reacting fraction is broken down by trypsin or 

 papain while the other fraction is not acted upon by proteolytic 

 enzymes. 



Classification of Standardization Methods. — An excellent dis- 

 cussion of present methods used in the standardization of tuber- 

 culin is included by Long* (1925) in his report of a new method of 

 assaying the strength of tuberculin by means of the "spermatocyte 

 reaction" in tuberculous guinea pigs. Long classifies the methods 

 in use at the present time as follows : 



"I. Hypersensitiveness of the Tuberculous Guinea Pig. 



1. The lethal dose. Method of : 

 Koch 



The Institute for Experimental Therapy, Frankfurt 



a. M. 

 The United States Bureau of Animal Industry. 



2. The skin test. 



Method of Lewis and Aronson. 

 "II. Antigenic Capacity of Tuberculin in Serum Reactions. 



1. The precipitin test. 



Method of Dreyer and Vollum. 



2. The complement-fixation test. 

 Method of Watson and Heath. ' ' 



The following description of these methods is based upon Long 's 

 report. 



Koch's Method. — The discoverer of tuberculin according to 

 Long, "considered a preparation of tuberculin satisfactory if 

 0.5 c.c. or less would kill in six to thirty hours, with characteristic 

 pathologic change, a guinea pig infected one month previously 

 with tuberculosis. ' ' 



Method Used ix the Institute of Experimental Therapy, 

 Frankfurt. — This is a modification of Koch's method sug- 

 gested by Doenitz (1921). A large number of guinea pigs, 

 fifty or more, are infected with tubercle bacilli. After defi- 

 nite symptoms of the disease develop two series of six guinea 

 pigs each are selected. One series is injected subcutaneously with 

 varying amounts of Koch's OT while the second series is injected 

 with corresponding amounts of the tuberculin to be standardized. 



♦Long: J. Infect. Dis. 37: 368, 192.5. 



