430 Major P. S. Leiean [April 23, 



catches sight of the seething mass of motile organisms he blenches ; 

 and one has the satisfaction of seeing him pass straight on into the 

 inoculation room. 



The explanation of the process in less simple, and matters must 

 be put in a way which appeals to his imagination. There is no better 

 way than by adopting the simile of the battlefield, somewhat on these 

 lines : The organisms are the enemy invaders ; the body the invaded 

 country ; the toxins the enemy's projectiles ; the complement the 

 unarmed population ; the tissue-cells the arsenals ; £he anti-toxins 

 the defenders'- projectiles ; the amboceptors the bayonets of the 

 defenders ; the phagocytes the " body-snatchers." 



With these pieces one fights a war-game for the men, illustrating 

 it by the diagrams as in Fig. 1, or by the working model now to be 

 demonstrated. 



Successful invcision. Unarmed defenders driven back by gun-fire 

 (negative chemiotaxis and toxins). Arsenals put out of action (toxins 

 kill tissue-cells). Capture of lines of communications (blood vessels). 

 €apital reached (heart). Surrender of defenders (death). 



Rally. The invaders' fire checked (anti-toxins). Defenders 

 armed (amboceptors). Defenders converge on invaders (positive 

 chemiotaxis). 



Battle joined. Invaders' fire smothered (toxins neutralized). De- 

 fenders getting in with the bayonet (complement and amboceptor). 



Victory. Invaders penned and annihilated (abscess cavity). Dead 

 of both sides (organisms and complement) removed by body-snatchers 

 (phagocytes). Invasion defeated. 



Permanent mobilization. Defenders armed with bayonets which 

 never become obsolete (the amboceptors — permanent). Shells for 

 guns becoming obsolete (transient anti-toxins). Enough bayonets 

 remain to enable defenders to crush any subsequent invasion before 

 the enemy can develop gun-fire (permanent immunity by bacteriolysis 

 before toxins can paralyse the defence). 



B. — Applicatiox of General Principles of Immunity 

 TO Anti-Enteric Prophylaxis. 



Having considered the general principles of immunization, we 

 have now to deal with their application to the problem of protecting 

 our men against enteric fever. 



Initial difficulties were experienced in many ways. 



1. The view then held as to the immunity of animals to true 

 enteric (a view since modified by experiments on anthropoid apes) 

 led to its being thought necessary for all experimental work to be 

 carried out on man. This factor also made it impossible for passive 

 immunization to be undertaken as a curative measure in developed 

 human enteric : as immunized animals produce no amboceptors, but 



