SUPERSENSITIVENESS OB ANAPHYLAXIS 597 



After this brief review we may consider some of the 

 phenomena of serum anaphylaxis, as it is now called. In its 

 study horse serum has been chiefly employed, but other sera are 

 also efficient, and the guinea-pig is the most suitable test animal ; 

 the rabbit has also been used, but its relative susceptibility is 

 less than a hundredth of that of the guinea-pig. In the case of 

 mice it is difficult if not impossible to bring about serum ana- 

 phylaxis. There is first of all the sensitising injection; a guinea-pig 

 is injected subcutaneously with a minute quantity, e.g., '001 c.c. 

 of horse serum, though even '000,001 c.c. has been found 

 sufficient; other methods of injection may also be employed. 

 After a certain number of days, usually twelve as a minimum, 

 anaphylaxis has been established, and the test for this is usually 

 made by injecting subcutaneously 5 c.c. of horse serum. In 

 the anaphylactic animal severe symptoms occur; restlessness 

 and hyperalgesia are followed by evidence of collapse, the 

 temperature falls markedly, urine and feces are passed, the 

 heart's action becomes weak and the respiration embarrassed : in 

 fatal cases respiration stops before the heart's action ceases. The 

 intravenous injection of a smaller amount of serum brings about 

 the same result more rapidly. It is to be noted that the 

 minimum amount of serum necessary to bring about the 

 symptoms of fatal anaphylactic shock is much greater, about a 

 thousand times greater, than the original sensitising dose ; and 

 that while anaphylaxis is not fully established till about the 

 twelfth clay, its gradual development can be shown by disturbance 

 of the temperature at a much earlier period on re-injection of 

 serum. Anaphylaxis has the character of specificity, apparently 

 within corresponding limits to immunity (p. 558) ; that is, it is 

 manifested only on the re-injection of the same protein substance 

 as that used in the first instance. There is also a passive ana- 

 phylaxis, as is shown by the fact that if a certain amount of the 

 serum of an anaphylactic guinea-pig be injected into a normal one, 

 the latter becomes anaphylactic, so that the characteristic symptoms 

 appear in it when the test amount of horse serum is injected. In 

 most instances an interval of some hours at least must, however, 

 elapse between the injections in the guinea-pig (Otto) ; if the 

 two injections are made at the same time there is usually no 

 result. In the rabbit and dog, however, the symptoms appear 

 almost at once after the two injections. Passive anaphylaxis 

 usually disappears after a few weeks at longest, whereas active 

 anaphylaxis has been observed after more than two years ; here 

 also there is an analogy between anaphylaxis and immunity. 

 Another interesting observation has been made, namely, that the 



