64 THE DEFENSIVE FORCES OF THE MACROO'RGANISM 



serum. As the leukocytes from other infectious diseases (appendi- 

 citis and puerperal sepsis) showed a similar behavior toward pneumo- 

 cocci, Rosenow concluded that this difference is essentially the 

 expression of an increased power of resistance and higher activity 

 on the part of the younger cells which find their way into the circu- 

 lation in acute septic processes, and which in normal blood are in the 

 minority. Differences of this order must unquestionably exist, but 

 they have, after all, but little to do with the question whether the 

 leukocytes as phagocytes play only a secondary role in the defence 

 of the infected organism against the invading bacteria. The greater 

 part of the evidence is certainly in favor of this view; the existence 

 of substances which directly influence leukocytic action (stimulins, 

 in the sense of Metschnikoff) has at any rate not been satisfactorily 

 demonstrated. 



Effect of Opsonification on Bacteria. Of the manner in which opsoni- 

 fication prepares bacteria for phagocytosis we know nothing that is 

 definite. If we accept the view of Michaelis, that ameboid cells react 

 to stimuli, which affect their surface locally, by a local saponification 

 of their lipoid membrane (ectoplasm), and that this leads to local 

 changes of surface tension, which in turn are followed by mechanical 

 surface distortions which we designate as ameboid movements, 

 then we may imagine that the primary effect of the opsonins and 

 tropins upon bacteria may be such that the bacterial surface is so 

 influenced chemically (sc., chemically-physically) that its contact 

 with the lipoid ectoplasm produces the same effect which normally 

 emanates from the body of the leukocyte itself. But this, after 

 all, tells us very little that is tangible. So much, however, is cer- 

 tain, that opsonification in itself does not impair the vitality of the 

 bacteria. 



While the discovery of the opsonins and tropins has materially 

 aided our conception of the general mode of action of the leukocytes, 

 and has demonstrated the relative dependence of the latter upon the 

 presence of the former insofar as the actual process of phagocytosis 

 is concerned, we are still in comparative ignorance of the mechanism 

 by which leukocytes are attracted toward certain bacteria and other 

 organisms. That this actually occurs is a matter of daily observa- 

 tion, every abscess formation being a demonstration of the event; 

 for pus corpuscles are nothing else than polynuclear neutrophilic 

 leukocytes which have emigrated from the bloodvessels to the seat of 



