ON THE NATURE OF OPSONINS. 391 



vinced myself of the fact that fresh frog serum produces com- 

 pletely hemolysis of bovine blood corpuscles previously treated 

 with an inactivated specific serum (rabbit > bovine). If, then, the 

 anthrax opsonin of frog serum were identical with the alexin, the 

 latter, after having been fixed on bacteria, should no longer be 

 capable of hemolyzing sensitized red blood corpuscles. The entire 

 experiment with the controls was arranged as follows: 



A. Into each of 6 very small tubes a drop of thick emulsion 

 of anthrax bacilli (24-hour agar culture) was placed, together with 

 vo, ?V, wu, riu, ?ho and g-io of a cubic centimeter of fresh frog 

 serum. These were properly mixed, left for one-half hour in contact 

 and then centrifugalized. 



B. In G similar tubes containing each 0.5 of a cubic centimeter 

 of a 5 per cent suspension of bovine blood corpuscles saturated with 

 hemolytic sensitizer was placed one drop of each supernatant fluid 

 from the tubes in "A" series. 



C. Equal volumes of the washed bacilli from "A" series were 

 mixed with an emulsion of thrice-washed frog leucocytes. A com- 

 parison was then made of the degree of phagocytosis in " C," 

 which may begin at once, with the degree of hemolysis which 

 appears in " B " after considerable time. 



D. As a control, G tubes were arranged containing each 0.5 of a 

 cubic centimeter of the same emulsion of sensitized blood cor- 

 puscles as in " B," and to each is added one drop of equal volume 

 containing, respectively, 2V, ?V, so, ifo, sio and j^o of a cubic 

 centimeter of fresh frog serum which was not previously 

 treated with anthrax bacilli. The result of this experiment is as 

 follows : 



1. The intensity of phagocytosis in " C " decreases from tube 1 

 to 6. In No. 1 the phagocytosis is very marked, in No. 6 none is 

 apparent. This is evident, since the bacilli fixed less opsonin as 

 the serum dilution increased in " A." 



2. In"B," hemolysis appears in none of the tubes. The reason 

 for this might be that the dilution of serum in " A " was too great 

 to show any appreciable alexin action. This, however, is not so, 

 because : 



3. In "D" series there is hemolysis in the first four tubes, which 

 grows progressively less, and in the last two there is none. (In 



