INFECTION AND IMMUNITY 165 



such an injection there is a sudden liberation of 

 large amounts of toxic material. The parent eral 

 introduction of large quantities of alien proteid 

 must, however, be very exceptional under natural 

 conditions. The number of bacteria primarily 

 involved in an infection certainly represents but a 

 very small amount of alien proteid. If the body is 

 in the condition of allergy (anaphylaxis) at the 

 time of infection it will be able to respond more 

 quickly than otherwise and perhaps destroy the 

 invaders. Under these circumstances it is con- 

 ceivable that the condition is really an immunity 

 reaction. Looking at the entire question broadly 

 we may regard the mechanism which lies at the 

 bottom of the phenomenon of anaphylaxis as a 

 useful contrivance which enables the organism to 

 rid itself of alien proteid, both organized and un- 

 organized, which has been introduced parent erally. 

 Immunity Reaction on the Part of Bacteria. It 

 may be well at this point to call attention to a view 

 advanced by Welch some years ago. According to 

 this it is reasonable to suppose that just as the 

 animal body produces antibodies against an invad- 

 ing organism, so does the latter, owing to the action 

 of the body fluids, produce antibodies directed 

 against the tissues of the invaded body. In this 

 way the infecting organism would be adapting itself 

 to unfavorable surroundings, and this we know it 

 often does. It is certain that the animal body often 



