394 STUDIES IN IMMUNITY. 



This experiment shows, therefore, that the opsonin disappear 

 to a great extent from the serum together with the alexin. 



I should like to cite a final experiment upon the binding or fix- 

 ation of alexin in support of the conception of the identity of normal 

 opsonin and alexin. It is well known that rabbit blood is strongly 

 hemolyzed by fresh dog serum. If suitable doses are used, the rabbit 

 blood corpuscles will fix all the normal sensitizers and all the alexin 

 of the dog serum. This fact is made use of in the following experi- 

 ment: 



Tube 1. 0.2 of a cubic centimeter of normal defibrinated rabbit 

 blood is washed three times with physiological saline solution. 

 After the third washing all the supernatant fluid is removed with a 

 pipette. To the centrifugalized blood corpuscles is added 0.2 of a 

 cubic centimeter of fresh dog serum and 2 drops physiological 

 saline solution. They are properly mixed and allowed to remain 

 in contact 2 hours. 



Tube 2. 0.2 of a cubic centimeter of a thick emulsion of anthrax 

 bacilli (24-hour agar culture) plus 0.2 of a cubic centimeter of 

 fresh dog serum and 2 drops of physiological saline solution, 

 mixed, and left in contact 2 hours. After 2 hours both tubes are 

 centrifugalized. In tube No. 1 a marked hemolysis has taken 

 place. As a control to determine the content of alexin in the fluid 

 of tube 2, the following three tubes are made: 



A. 0.5 of a cubic centimeter washed rabbit blood ; 1 drop of 

 fresh dog serum. 



B. 0.5 of a cubic centimeter washed rabbit blood; 1 drop of 

 fluid from tube 2. 



C. 0.5 of a cubic centimeter washed rabbit blood; 1 drop of 

 physiological saline solution. 



Contact, 2 hours. 

 Result: A. Hemolysis. 



B. Faint hemolysis, distinctly less than in A. 



C. No hemolysis. 



The hemolysis in "A" is naturally less than in tube 1 because in 

 the latter tube equal parts of blood and serum had been brought 

 together and the dilution of the serum in "A" is therefore much 

 greater. The important point is that the weaker hemolysis in " B " 

 proves that in tube 2 a fixation of alexin on the bacteria has taken 



