504 THE WONDER OF LIFE 



horse-serum without showing any signs of disturbance, 

 a month later succumbed at once on receiving an injection 

 of one-twentieth the quantity of the original amount. 



Anaphylaxis is invariably specific. That is to say, an 

 animal which has been rendered hyper-sensitive to one 

 particular substance, is not affected in any peculiar way by 

 a subsequent injection of another substance, not even by 

 a different kind of blood-serum. This has a curious appli- 

 cation in the practice of medical jurisprudence. It supplies 

 a new and conclusive method of determining the source of 

 a quantity of blood, for instance whether it is human or 

 not. Suppose there be in readiness a set of guinea-pigs 

 which have been treated, a month or so before, with large 

 doses of the serum of different creatures man, dog, horse, 

 and so on ; a solution of the blood to be identified is 

 injected into each of them ; one reacts and the others 

 remain unaffected ; the blood to be identified came from 

 the kind of organism whose serum had been injected 

 into the guinea-pig which reacted. 



Another remarkable experiment was made with guinea- 

 pigs for here, as in other cases, this stupid rodent justifies 

 its existence by proving a remarkably fine subject for 

 experiment. Its sensitiveness to a given substance may 

 be increased five thousand times, which makes very delicate 

 testing possible. The experiment was that of injecting 

 into a set of guinea-pigs an extract of the muscle of a human 

 mummy, and after an interval other muscle extracts from 

 various organisms. But the guinea-pigs proved the 

 specific nature of anaphylaxis, they reacted only to extract 

 of human muscle, ' thus proving, if proof were needed, that 

 the chemical constitution of the human body has not 

 notably varied in the last three or four thousand years '. 



