INTRODUCTION 15 



against cholera. Wright's work, however, marked a 

 new epoch, since he demonstrated that antibodies may 

 be produced by inoculation with dead bacteria. The 

 following year, Haffkine immunized himself against 

 the plague by inoculation with a sterilized culture of 

 B, pestis. Up to this time, bacterial inoculations on 

 the human had been employed solely in a prophylactic 

 capacity. Wright enjoys the distinction of being the 

 first to realize that any bacterium responsible for local 

 disease and capable of isolation in pure culture may 

 be employed in the form of a bacterial suspension or 

 bacterin to cure the disease it causes. 



Seven years later, Wright and Douglas, taking ad- 

 vantage of Leishman's studies on comparative phag- 

 ocytosis, showed that phagoc}i;osis does not occur save 

 in the presence of serum, thus claiming a specific sensi- 

 tization of bacteria by certain substances in the blood- 

 serum to which the name " opsonins " was given. An 

 ingenious and clever laboratory method was devised 

 whereby the measure of the ratio of phagocytability 

 could be determined and this was styled the " opsonic 

 index." The work of Wright attracted universal at- 

 tention and popularized active immunization by bac- 

 terin therapy to an unprecedented and world-wide 

 extent. 



Synchronously with Wright's studies, the discov- 

 eries and advances in serology were truly remarkable. 



