THE WONDER OF LIFE 505 



The medical aspects of anaphylaxis do not concern us 

 here, but we may note that Professor Richet regards the 

 phenomenon as throwing hght on the diagnostic value of 

 tubercuUn, and probably also on the occasional terrible 

 accidents which for a time almost discredited it as a thera- 

 peutic agent. This latter point is still under investigation. 

 The ' serum disease ', too, which sometimes follows the 

 use of anti-toxin and inoculation for plague is probably 

 to be explained in the same way. Cases are described 

 which seem to show that a substance may be prophylactic 

 against a particular disease, bringing about a condition of 

 immunity, and, at the same time, anaphylactic against 

 itself, inducing hyper-sensitiveness to even smaU doses. 

 The simultaneous development of immunity and anaphy- 

 laxis may serve to illustrate what we mean by the 

 subtlety of hfe. From a practical point of view it is 

 comforting to learn that the physiologists have already 

 devised an ' anti-anaphylactic method of procedure '. 



No crystaUizable substance is known to produce anaphy- 

 laxis, but almost any colloid substance (i.e. an albuminoid 

 unable or hardly able to pass through organic membranes) 

 may do so under certain conditions. Among these con- 

 ditions are, that a certain time — an incubation period — 

 must elapse between the doses, and that the substance 

 — serum, egg, milk, muscle-extract, vegetable extract, 

 sea-anemone extract, or whatever it may be — must be 

 introduced into the circulation. ' Alimentary anaphy- 

 laxis ', i.e. through eating the substance in question, seems 

 to come about very rarely, and the reason for this is obvious, 

 since it is not the substance itself, but the result of the 

 digestion of the substance, that passes from the food-canal 

 into the circulation. But the rare exceptions are of great 



