INTRODUCTION 3 



Has the serum injected accidentally turned out to 

 be toxic ? No, for when it has been injected into 

 other individuals who have never previously received 

 any inoculation, no ill-effects, either local or general, 

 have resulted. 



What, then, is the cause ? It is anaphylaxis. 



Instances of this nature are observed with mathe- 

 matical regularit}^ in the guinea-pig. If we merely 

 inject a guinea-pig, subcutaneously or otherwise, 

 with a minimal dose of horse serum, say about 

 o-oi c.c, the animal from the moment of this opera- 

 tion becomes " marked " for the rest of its days. If 

 after the lapse of some time — a fortnight, six months, 

 or a year — we give this same guinea-pig an intra- 

 venous, intraspinal, or subdural injection of o-i c.c, 

 of the same serum^that is, a dose which is absolutel)^ 

 harmless to anj^ ordinary guinea-pig — symptoms of 

 extreme gravity immediately make their appearance 

 The animal is seized with convulsions which increase 

 in severity; signs of paralysis immediately appear, 

 followed in a few minutes by cessation of respiration 

 and terminating in death. 



What invests these anaphylactic phenomena with 

 so mysterious a character is the fact that they are set 

 up by substances that are entirely anodyne in nature. 

 This upsets our ideas as to the harmfulness or the 

 reverse of the substance. For instance, we inject an 

 animal subcutaneously with an extremely weak, 

 almost infinitesimal dose of milk or egg-albumen. 

 Six months or a year later the same guinea-pig is 

 inoculated with a dose of milk or egg-albumen that 

 would not cause a normal guinea-pig to move a 

 muscle. Barely two to three minutes have elapsed 

 from the time of operation before the animal becomes 

 overwhelmed. What is so astonishing is the fact 

 that non-toxic substances assume so formidable 

 toxicity in animals that have already been injected 



