62 VACCINE AND SERUM THERAPY. 



ultimate return to the normal. These changes in the number of 

 leococytes they find precede the changes in the opsonic index. 

 When the index is at its height the number of leucocytes has re- 

 turned to the normal. Various methods designed to increase the 

 number of leucocytes have been resorted to but have all been of little 

 avail in increasing the opsonin content in the blood as determined 

 by Wright's opsonic index. If, however, the leucocytes can be 

 stimulated to phagocytosis an increase in the number of leucocytes 

 in the infected region must certainly be of value. Opsonins are 

 by some supposed to originate in the leucocytes. The importance 

 and possibility of this becomes more evident from the work of 

 Peterson and Hiss and Zinsser. Potter believes that the opsonic 

 index varies with the source of leucocytes. 



RELATION OF OPSONINS TO STIMULINS. 



Metchnikoff has described a series of experiments in which 

 the introduction of serum, either from normal or immunized ani- 

 mals, greatly increased phagocytosis. This action, he supposes, 

 is exerted on the leucocytes and is of great importance in phago- 

 cytic immunity. The substance in the serum which he regards as 

 stimulating leucocytes he calls "stimulin." Stimulins are prob- 

 ably the same as opsonins, even though up to the present time, 

 in the observations reported, their action is on the leucocytes and 

 not on the bacteria. 



OPSONINS AND AGGRESSINS. 



Endotoxins or the aggressins of Bail, have by some been sup- 

 posed to account for decreased phagocytosis or low opsonic in- 

 dices obtained with some sera. Aggressins are supposed to injure 

 the leucocytes and inhibit their action. The part the endotoxins 

 play in preventing phagocytosis has not yet been determined. 

 Dorr, Sauerbek and others have shown that aggressins are not 

 difinitely specific. Neufeld from experiments has decided that 

 the lack of phagocytosis with virulent organisms does not depend 

 upon the injury to leucocytes and for this reason does not believe 

 that decreased phagocytosis is due to the action of aggressins. 



