OPSONIC INDEX. 549 



determined by the effect which an injection has on 

 the opsonic content of the patient's serum. If a 

 suitable dose has been given, there occurs a short 

 negative phase in which the opsonins are decreased 

 in quantity, and this is followed by a rather pro- 

 longed positive phase when they undergo an in- 

 crease. If too large a dose is given, the negative 

 phase is exaggerated and prolonged. In many in- 

 stances it has been noted that improvement and 

 recovery go hand in hand with an increase in the 

 opsonins. As in streptococcus infections the total 

 resisting power of the body depends on the varia- 

 tion in the capability of the leucocytes to take up 

 and digest cocci as well as the opsonic action of 

 the serum. 



The normal serums of man and many animals 

 may agglutinate the staphylococcus, but with no 

 constancy. In one instance human serum aggluti- 

 nated in a dilution of 1-100 (Kraus and Low), 

 and normal goat serum in a dilution of from 

 1-50 to 1-400 (Amberger, cited by Neisser). The 

 serums from cases of staphylococcus infection 

 (e. g., osteomyelitis) and of highly immunized an- 

 imals undergo an increase in the quantity of ag- 

 glutinins. The agglutination usually is strongest 

 for the homologous strain, and if other strains are 

 agglutinated equally it signifies a close relation- 

 ship to the homologous strain. 



From the fact that only pathogenic strains pro- 

 duce hemolysin and leucocidin, Neisser and 

 Wechsberg considered them specifically different 

 from non-pathogenic strains. This view is borne 

 out by the results obtained with the agglutination 

 test. Serums obtained by immunization with 

 pathogenic strains have a much higher aggluti- 



