392 STUDIES IN IMMUNITY. 



these latter cases the serum dilution was actually too great.) This 

 experiment tells us, therefore: 



(a) That the alexin was fixed at the same time with the opsonins ; 

 (b) that the intensity of the action o opsonin and alexin decreases 

 equally with increasing serum dilution. The parallelism between 

 the action of opsonins and alexins is therefore striking. 



I have tried the reverse experiment in order to convince myself 

 whether a normal serum which has previously been brought together 

 with a suitable amount of sensitized blood corpuscles, in order to 

 bind the complement, has lost its opsonin together with its alexin. 

 It might be that the hemolysis, which occurs after addition of fresh 

 alexic serum to sensitized blood corpuscles, might influence the 

 later phagocytosis experiment with this serum and check its 

 opsonic action. This consideration led me to employ fresh horse 

 serum, the alexin of which, as is well known, becomes fixed upon 

 sensitized blood corpuscles readily without causing hemolysis. 

 Furthermore, I had previously convinced myself that horse serum 

 exerts a pronounced opsonic effect when added to anthrax bacilli 

 and washed frog leucocytes. The technic of the experiment is as 

 follows : 



Tube A contains 2 c.c. of a 5 per cent emulsion of bovine cor- 

 puscles (thrice washed) and 0.2 of a cubic centimeter of inactivated 

 specific hemolytic serum (rabbit > bovine). 



Tube B contains the same amount of blood as "A" and 0.2 

 of a cubic centimeter of physiological saline solution. 



The tubes are properly mixed and allowed to stand a quarter of 

 an hour. The tubes are then filled up with saline solution, shaken, 

 centrifugalized and all the supernatant fluid carefully removed 

 with a pipette. To the sediments in the two tubes is then added 

 0.2 of a cubic centimeter of physiological saline solution and 0.1 

 of a cubic centimeter of fresh horse serum. They are shaken and 

 the mixtures allowed to stand for 2 hours. They are then cen- 

 trifugalized, and the supernatant liquids are employed for the fur- 

 ther tests. It is evident that if the quantities have been properly 

 chosen (and such is the case here) all the alexin of the horse serum 

 in tube "A" has been bound by the sensitized blood corpuscles, 

 whereas, in tube "B" it is still free in the fluid. As a definite con- 

 trol we may employ a phenomenon which has given rise to a dispute 



