PART III 



ON THE ANTI-BACTERIAL PROPERTIES 

 OF SERUM 



I. OPSONIC ACTION 



(a) ON THE COMBINING PROPERTIES OF OPSONINS 

 OF NORMAL SERUM 



Since the publication of the original paper by Wright 

 and Douglas l on opsonins much important work has been 

 done on the subject, and many important facts have been 

 ascertained. The result has been to establish the cardinal 

 part played by opsonic substances in the phenomena of 

 phagocytosis, and also to supply a means of estimating 

 the degree of immunity in one of its aspects. It must be 

 admitted, however, that much doubt still exists as to the 

 biochemical position of the substances in question. Is 

 there, for example, a single type of substance which is 

 thermolabile like bactericidal complement, and which 

 increases during the process of immunization, or are there 

 at least two classes of substances, one of which is thermo- 

 labile and another thermostable, and if so, what is the 

 relation of these to each other ? Among the phenomena 

 of immunity already known, we have, on the one hand, 

 certain effects produced by what, so far as is known, are 

 single substances, of which agglutinins may be taken as 

 the type ; and, on the other hand, effects which are due 



1 Wright and Douglas, Proc. Roy. Soc., London, vol. Ixxii, p. 357. 



