PHAGOCYTOSIS 287 



ham and Bulloch, who found that when the number of leucocytes 

 in the blood was increased by injections of cinnamate of sodium, 

 there was an increase in the complement, but not in the 

 opsonin. 



It may be pointed out that if opsonin and complement are the 

 same, we must suppose that the opsonin test is the most delicate 

 method of demonstrating this substance that we have, since 

 phagocytosis may be facilitated by substancesfwnicnjji} comple- 

 ments cannot be detected by ordinary tests. Further, we must 

 assume that it unites with bacteria direct, and sensitizes them for 

 phagocytosis without the intervention of amboceptor. There is 

 no serious difficulty in accepting both suppositions. 



Lastly, Muir has shown that the substances which have the 

 power of absorbing complement (such as compounds of red blood- 

 corpuscles and their amboceptor) also remove the thermolabile 

 opsonin. We are forced, therefore, to the conclusion that com- 

 plements may play the part of opsonins. But to do this we must 

 necessarily broaden our ideas of the complements, and attribute 

 to them some degree of specificity ; otherwise the opsonic index of 

 any given sample of serum as measured against a given control 

 should be always the same, which, as we have already emphasized, 

 is not the case (see footnote, p. 286). 



These results suggest another train of ideas as to the role of 

 bacteriolysis in immunity. We have already seen reason to 

 believe that this is not of the greatest importance, and have found 

 it difficult to think that so elaborate a mechanism should be of so 

 little apparent use. May it not be that the complements are 

 specially intended for use as opsonins, and that their action in 

 bacteriolysis is a secondary one, and comparatively of less 

 importance ? This, of course, is a close approximation to Metch- 

 nikoff's views, but there is this difference : his cytase is a 

 digestive ferment which, in the case of microcytase, is adapted to 

 attack all sorts of bacterial proteid. But with the opsonins or 

 complements we must assume that different molecules occur 

 which have different combining affinities for the protoplasm of 

 different bacteria, or, in other words, which differ slightly in their 

 haptophore groups. Yet this difference is one in degree and not 

 in kind, for they all have some power of uniting with all bacteria, 

 and a great power of uniting with the bacterium-amboceptor 

 combination. 



On this theory the appearance of amboceptor will take on a new 



