200 A MANUAL OF BACTERIOLOGY 



that the ultimate result is as though a small sensitising 

 dose had been injected. The first dose, or series of doses, 

 of antigen inducing the sensitive state is known as the 

 sensitising dose ; the second dose of antigen causing the 

 effect is known as the reacting or toxogenic dose. 



The cardinal features of anaphylaxis are (1) Any anti- 

 gen will cause it, e.g. serum, egg white, toxins, etc. ; (2) the 

 sensitising and toxogenic doses must be of the same kind 

 of antigen, e.g. horse serum and horse serum ; thus a first 

 dose of horse serum followed by a second dose of sheep 

 serum would not induce anaphylaxis. Closely allied pro- 

 teins may cause some reaction ; (3) the amount of antigen 

 given may vary within wide limits without definitely 

 influencing the severity of the effect ; (4) sensitisation is 

 usually produced in from twelve to fourteen days after the 

 administration of the sensitising dose, never before ; with 

 massive sensitising doses it may be delayed for a period 

 up to six weeks ; (5) sensitisation once induced may exist 

 for years ; (6) reaction having occurred, the animal is 

 desensitised and no longer sensitive ; (7) extremely 

 email doses of antigen will sensitise, even 0-000001 c.c. 

 of serum, though apparently there is no limit in the other 

 direction ; (8) ansesthetisation when the toxogenic dose of 

 antigen is given prevents the development of symptoms. 



Animals vary greatly in the ease with which they are 

 sensitised. The guinea-pig, horse and goat are very 

 readily sensitised ; the rabbit, dog and probably man are 

 less susceptible ; the mouse is almost or completely 

 refractory. Sensitisation may be induced by any route 

 which ensures the penetration of the antigen in a rela- 

 tively intact state. The digestive tract, therefore, 

 usually fails unless large quantities of the antigen are 

 given. In the case of the toxogenic dose, antigen ad- 

 ministered by the mouth or rectum rarely induces 

 anaphy lactic shock ; the most certain methods are intra- 



