NATURE OF OPSONINS 259 



is thermostable and is strictly specific. On these and 

 other grounds it is considered by many that opsonins 

 are not separate and distinct anti-bodies, but that normal 

 opsonin is a complement and immune opsonin is an 

 amboceptor. 



It is generally considered that opsonins play an im- 

 portant part in processes of immunity, especially in 

 aiding resistance to infection by promoting phagocytosis. 

 They are more active in some infections than in others, 

 especially in conditions in which phagocytosis is the chief 

 defensive mechanism, as in pyogenic infections. 



It is doubtful, however, if opsonins are present in more 

 than traces in the unaltered blood plasma, : like alexins, 

 they seem to develop as a result of coagulation. The role 

 of opsonins in immunity and in recovery from infection is 

 therefore a complex problem. 



Method of Determining the Opsonic Index 



The requisites are: (1) Wright's pipettes with india-rubber 

 teats ; (2) the serum of the patient to be tested ; (3) the serum of 

 a healthy person for a control ; (4) a suspension of the organism 

 for which the determination is to be made ; (5) a suspension of 

 living leucocytes. 



1. Wright's pipettes with india-rubber teats. These are made of 

 glass tubing of the form shown in a, Fig. 36, which is about two- 

 thirds full size. Glass tubing must be chosen which properly fits 

 the teats. The capillary portion should have a bore of about 

 T \ in. The tip should be slightly contracted as shown in b ; this 

 prevents the column of fluid in the tube moving so quickly. A 

 throttled pipette (p. 60) may be used. 



2 and 3. The Sera. These two specimens should be taken at 

 about the same time, and the determination should be made as 

 soon as possible. 



The blood is preferably collected in a Wright's capsule (Fig. 36, 

 d). Both ends of the pipette are broken off, and the blood is 

 collected by immersing the bent end in the blood as it runs from a 

 prick made with a Hagedorn or triangular needle in the ear or 



172 



