THE PHYSICAL ASPECT OF THE 

 OPSONIC EXPERIMENT 



By MAJOR A. G. McKENDRICK, M.B., Ch.B., F.R.S.E. 



Indian Medical Service 



The recognition of the principle that prevention is better than 

 cure, obvious though it may seem, has of late years exercised 

 a considerable influence on medical research. Side by side with 

 the development of preventive sanitation has advanced the 

 investigation into the reasons why infection is escaped by 

 certain individuals. The importance of leucocyte and serum as 

 protective agents has been fully established, and the reinforce- 

 ment of their potency by vaccine therapy, general hygiene, and 

 the like, has led to the foundation of a new school of medical 

 practice. That the serum alone may overcome the intruding 

 microbe of disease is an accepted fact, and the discovery by Sir 

 Almroth Wright of its important role in the vital phenomenon 

 of phagocytosis has still further focussed attention on it. As 

 the serum is a fluid, and as a fluid can hardly be credited with 

 vital activity, the part which it plays in the process of immunity 

 is capable of investigation by the methods of physics and 

 chemistry. On account, however, of the complex nature of the 

 substances involved, little advance has been made by purely 

 chemical methods. In place of these, the mathematical methods 

 of physical chemistry which deal with velocities of reaction, and 

 equilibrium states, have been applied, and in this direction con- 

 siderable progress has been made by Arrhenius and others. 

 Thus in this case at least the application of mathematics has 

 been of service to medicine. But immunity does not depend on 

 the serum alone. The leucocyte is, as I have said, a factor in 

 the destruction of the intruding microbe, and it is with this 

 aspect of the question that I propose to deal. 



The phenomenon of phagocytosis as it applies to disease 



497 



