42 IMMUNE SERA 



bacilli other than toxin, it will also appear on the 

 second arm. 



An interesting application of the Schick reaction 

 is that recently introduced by Neisser for determin- 

 ing the virulence of diphtheria bacilli in a shorter 

 time than has heretofore been possible. Still more 

 recently, Zingher l has improved the technique of 

 Neisser so that four and sometimes six cultures may 

 be tested on two guinea pigs. Zingher's method is 

 as follows: A twenty-four-hour culture of the diph- 

 theria bacilli grown on Loeffler's medium is washed 

 off with 20 cc. of normal saline; ^ of a cc. of this 

 suspension is injected intracutaneously on the 

 abdominal surface of a large guinea pig. It is 

 sometimes possible to make four such injections 

 into one pig. A second pig is given 8 cc. of diph- 

 theria antitoxin of the strength of 500 units per cc. 

 and similar injections of the same cultures made 

 into this pig. A reaction in the first pig should 

 occur in from twenty-four to thirty-six hours. 

 Pseudo diphtheria bacilli produce no reaction. The 

 pig which has received the antitoxin, should, of course, 

 show no reaction even with the virulent bacilli. 



The Preparation of Diphtheria Antitoxin. The 

 following account taken from Park shows the pres- 

 ent methods of producing diphtheria antitoxin. 



Production of the Diphtheria Toxin. A strong diph- 

 theria toxin should be obtained by taking a very virulent 



1 Zingher, Journal Infect. Diseases, Vol. xvii, No. 3, Nov., 1915. 



