BY R. GREIG-SMITH. 385 



critical review, coiicludes that the evidence is in favour of 

 opsonins and agglutinins having a similar structure. 



Agglutination requires the presence of salts to bring about the 

 phenomenon, and the same is probably true of opsonisation. They 

 are undoubtedly necessary for the observation of phagocytosis 

 because the leucocytes are destroyed in the absence of an isotonic 

 solution. The theories regarding the nature of opsonisation do 

 not take into account the salt which ma}'^ be necessary for the 

 opsonin to be fixed by (i.e., precipitated upon) the bacteria, in 

 order that the phenomenon of phagocytosis may take place. 



I. do nob think that the function of the salt in opsonisation has 

 ever been noted. It would not be an easy matter to obtain the 

 opsonin free from salt, and we certainly could not demonstrate 

 opsonisation without salt, for the phagocytes would be destroyed 

 in a salt-free medium. 



In considering the curve showing the action of dilution upon 

 the opsonic activity of the serum, it might be well to admit, as a 

 postulate, that the regular rise from infinity to the quarter dilu- 

 tion is due to the combined actions of the salt and opsonin, while 

 the depiessing substance, whatever it may be, is so dilute as to 

 be thrown out of action. All salts, however, have not the same 

 precipitating action. Chlorides are high in the scale, while 

 phosphates and organic salts are low; and it may be that the 

 depressing influence of the stronger percentage of serum is trace- 

 able to the presence of the latter. Upon the other hand, there 

 may be a certain amount of antiphagin or similar substance in 

 the serum. 



In the experiments from which Dean obtained his curves, the 

 average maximum number of cocci ingested per leucocyte varied 

 from 10 to 23. This number maybe considered to be high; as a 

 rule, one obtains more concordant duplicate results when the 

 maximum average is about five cells per leucocyte. With a 

 suspension of bacteria which would give this phagocytic index, 

 the curves might be different. Furthermore, the time of incuba- 

 tion will have a certain influence; there should be more irregu- 

 larity in the dilution-curves with longer periods of incubation*' 

 40 



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