FACTORS DETERMINING PHAGOCYTOSIS 323 



which in itself may furnish a slight amount of alexin or alexin-like 

 substances. 



We may regard the action of the immune serum upon the antigen 

 as rather a sensitization in the sense of Bordet, and it does not seem 

 logical to assume that the heat-stable bodies, similar in other respects, 

 are different merely because they can sensitize bacteria both to the 

 action of an alexin and to that of a living cell, which in itself surely 

 contains a number of different enzymes, comparable functionally to 

 alexin, though possibly not identical with it. 



Indeed, the experiments of Dean have given much positive evi- 

 dence in favor of regarding the immune opsonins or bacteriotropins 

 as true amboceptors or sensitizers. Dean 52 found that, although 

 heated immune serum may unquestionably opsonize by itself, its 

 action may be still further enhanced by the addition of a little diluted 

 normal serum (compare these results with those of Cowie- and Chapin 

 on normal opsonins). Hektoen' s 53 experiments with hemopsonic 

 immune sera are analogous. We cite one of these as illustrating the 

 point in question : 



TABLE I 



Phagocytosis of Goat Corpuscles under the Influence of Goat-blood-immune Rabbit 

 Serum, and Normal Guinea Pig Complement (Table from Hektoen, loc. cit.) 



Here, therefore, the diluted immune serum, but slightly cyto- 

 tropic in itself, was powerfully activated by a diluted unheated nor- 

 mal serum, which in itself was entirely inactive. 



Indeed, an experiment by Neufeld himself, with Bickel, 54 points 

 in the same direction. They found that, when a heated specific hemo- 

 lytic serum was added to the homologous cells in such small quanti- 

 ties that it no longer exerted cytotropic (opsonic) action, the addi- 

 tion of a small amount of alexin, too small to lead to hemolysis of 

 the cells (and not by itself cytotropic or hemopsonic), caused active 

 phagocytosis. Analogous experiments upon bacterial antisera were 

 carried out by Levaditi and Inmann. It thus appears that, even in 

 the case of the immune opsonins or bacteriotropins, we may think of 

 a participation of two substances a sensitizer-like one and one com- 

 parable to alexin or complement. We may, at least, infer that the 

 full opsonic action both of normal and immune sera is dependent 



52 Dean. Proc. Royal Soc. B., 79, 1907. 



53 Hektoen. Jour. Inf. Dis., Vol. 6, 1909, p. 67. 



*< Neufeld and Bickel. Arb. a. d. kais. Gesundh. Amt., Vol. 27, 1907. 



