514 IMMUNOLOGY 



In fact, Parker and others workino- in Zinsser's laboratory have 

 shown that so far as the precipitin reaction is concerned, it is 

 dependent upon an entirely different substance in the tuberculin 

 from that which elicits a positive skin reaction in tuberculous 

 animals. Furthermore, both complement fixing and precipitating 

 antibodies can be produced by injecting tuberculin into noi'nuil 

 animals, but such treatment does not produce tuberculin liypor- 

 sensitiveness such as is observed associated with active tuberculosis. 



Standardization by Long's Spermatocyte Reaction. — In this 

 test 10 animals are required. Eight are infected by injecting 

 one-half milligram of the Saranac laboratory strain R^ into the 

 groin. This leads to the development of a caseous nodule in the 

 regional lymph nodes within one month, but the process does not 

 become generalized. The animals are injected in duplicate with 

 0.01, 0.001, 0.0001 and 0.00001 mg., respectively, with the tuber- 

 culin to be tested. The two normal controls are inoculated with 

 the strongest dose. The volume of each dose is made up to 0.1 

 c.c. Injections are made into the middle of one testicle. The 

 reaction may be read after thirty-six hours or in from tw^o to 

 four weeks, the animals being killed and paraffin or celloidin sec- 

 tions prepared. 



Spermatocyte Tuberculin Unit. — The spermatocyte tuberculin 

 unit according to Long ''is that quantity of tuberculin just suf- 

 ficient to aboli.sh spermatogenesis in the majority of tubules on 

 injections of a volume of 0.1 c.c. into the testicle of a 400 gram 

 guinea pig with a mild localized tuberculosis of one month's dura- 

 tion. Microscopic se-ction of the testicle (middle cross-section) 

 one month after the injection of one unit or more shows the 

 majority of the tubules atrophic and lined only by spermatogonia. 

 No normal spermatocytes, spermatids, or spermatozoa are present. 

 The test is controlled by examination of the noninjected opposite 

 testicle and of the injected testicle of a noninfected animal, both 

 of which should show normal spermatogenesis. ' ' 



In Long's opinion this unit is useful in standardizing tuber- 

 culins for use in either therapeutic or diagnostic procedures. He 

 states that tuberculins such as OT and BE contain 10,000 and 

 1,000 spermatocyte units, respectively, per cubic centimeter. 



