162 THE PRINCIPLES OF IMMUNOLOGY 



showed minimal opsonic power and no hemolytic action. One protocol 

 from his work serves to illustrate. 



Heated immune serum Fresh guinea-pig serum Phagocytosis 



O.OOI 4 



O.OOI O.OI 2O 

 O.OI O 



Levaditi and Koessler showed that a serum which contained anti- 

 complement by virtue of immunization with complement, when added to 

 an immune opsonin, noticeably reduces the opsonic power. 



The full activity of the immune opsonin depends, as can be seen, 

 from the above experiments, upon a thermostable and a thermolabile 

 element, as is true of the normal opsonin, but the activation by fresh 

 serum in case of the thermostable element of immune opsonin is pro- 

 portionately much less than activation of thermostable normal opsonin 

 by fresh serum. Reference to the activation of a hemolytic amboceptor 

 by complement shows that a given amount of complement will activate 

 a very small amount of amboceptor in greater proportion than a large 

 amount of amboceptor. The thermostable fraction of opsonin has 

 been referred to as a facultative amboceptor, because the action of the 

 thermolabile part is not essential. Assuming this interpretation to be 

 correct and assuming that the thermolabile element operates as a com- 

 plement, it is a simple matter to infer that this complement would have 

 a proportionately larger action on the facultative amboceptor of normal 

 opsonin, which is present in very small amount, than on the similar am- 

 boceptor of immune opsonin, which is present in relatively large amount. 



Bacteriotropins. Neuf eld and his school maintain that the immune 

 opsonin is a body which operates only in the presence of complement 

 and that the tropins, bacteriotropins and cytotropins are bodies appear- 

 ing in serum which has been rendered complement-free, and which 

 exhibit a capacity for so altering bacteria or cells that they are easily 

 taken up by phagocytes. Levaditi and numerous other authors agree 

 that Neufeld has shown that the tropins are not identical with those 

 amboceptors which lead to cytolysis, but also agree that Neufeld has 

 not succeeded in demonstrating that the tropins are antibodies distinct 

 and apart from the thermostable element of immune opsonin. 



Opsonins for Cells other than Bacteria. Numerous substances, 

 including vegetable cells, such as yeasts, and bacteria, as well as a 

 variety of animal cells, may undergo phagocytosis when influenced by 

 opsonins. In connection with phagocytosis of animal cells the work of 

 Hektoen and his collaborators has been most extensive. The investiga- 

 tions have thrown much light on the general study of opsonins and, di- 

 rected particularly toward erythrocytes, have shown that the same 

 general laws governing the phagocytosis of bacteria operate in the 

 phagocytosis of erythrocytes. Neufeld and Handel have shown that 

 emulsions of fat droplets in protein-containing media can serve as 

 excitants of the formation of specific opsonic sera but conclude that in 

 these instances the protein capsule of the fat droplets which serves to 

 stabilize the emulsion is the important factor in the phenomenon. Led- 



