FERMENTATION 221 



The immunity once established endures a consider- 

 able time ; six months and possibly much longer. 



Ricin Antitoxine. Defibrinate the blood of the 

 immunized mice. Divide it into two portions. 

 1. To one portion add ricin solution in such a 

 ratio that the mixture shall contain YooVo 0' * e - 

 twice the fatal amount. 



Inject a fresh mouse subcutaneously with 1 c.c. 

 of this mixture per 20 grams of weight. 



The poison will be borne. It has been neu- 

 tralized by the serum of the immune animal. 

 This result accords with the discovery of Behring 

 and Kitasato that immunity in diphtheria and 

 tetanus depends on the power of the serum to 

 neutralize the poison. 



2. Divide the second portion of the antitoxine 

 blood among six small test-tubes. To the first 

 add a few drops yfjo^ Q"O r ^ n solution. To the 

 others add amounts increasing in a definite ratio. 



At first there will be no effect (immunity). 

 As the amount of ricin added is increased, a point 

 will be reached at which agglutination of red 

 corpusles will be produced. This is the neutrali- 

 zation point. 



Evidently, there is a definite quantitative 

 chemical relation between the toxine and the 

 antitoxine. 



