ON THE NATURE OF OPSONINS. 395 



place. The control with the fluid from tube 1 can, of course, not be 

 made up because hemoglobin has already been dissolved there. 

 The following opsonin experiments were furthermore carried out: 



1 . Washed dog leucocytes 



Anthrax bacilli [ Very marked phagocytosis. 



Fresh dog serum 



2. Leucocytes 1 



Anthrax bacilli > Weak phagocytosis. 



Fluid from tube 1 



3. Leucocytes 1 



Anthrax bacilli [ Slight phagocytosis. 



Fluid from tube 2 



4. Leucocytes as in 1, 2 and 3 

 Bacilli from tube 2 washed once 



No serum; merely some saline 

 solution. 



Very pronounced phagocytosis. 



The opsonin has, therefore, in great part disappeared from the 

 dog serum (2 and 3), together with the alexin, having become fixed 

 in tube 1 to the blood corpuscles (hemolysis) and in tube 2 to the 

 bacteria (4). 



All these facts lead us to the conviction that in the normal serum 

 the parallelism between the action of the alexin and the opsonin 

 goes so far that they can no longer be considered as different, but 

 must be regarded as identical. This conclusion agrees very well 

 with the frequently proven fact which has also been shown by me 

 to hold for frog serum, namely, that normal opsonin is thermolabile. 



I * have previously pointed out the difference between the op- 

 sonin and the agglutinin in frog serum for anthrax bacilli in that 

 they are destroyed at different temperatures (opsonin at 56, agglu- 

 tinin at 70). A further proof is found in tubes 5 and 6 of the 

 series on page 393. The differences in the degree of phagocytosis 

 are particularly large, here, whereas the extracellular typhoid 

 bacilli in the preparations of both tubes were slightly agglutinated 

 by the horse serum. 



In investigating the opsonins of specific sera I have employed 

 hemolytic sera. Savtchenko f has previously shown that blood 

 corpuscles that are loaded with specific hemolytic sensitizers easily 

 fall prey to the leucocytes 4 



* Loc. cit. 



f Annales de 1'Institut Pasteur, December, 1907. 



J One must remember that these experiments were performed with unwashed 

 exudate leucocytes, and other influences cannot be excluded, 



