" REACTIONS " AND SIMILAR PHENOMENA 313 



period. After an injection of yj^ c.c. or ^4^ c.c. the animal is 

 hypersensitive in a fortnight or less, whereas after a dose of 8 c.c. 

 the sensitiveness does not reach its maximum for some forty-five 

 days. The duration of this anaphylaxis is not exactly determined, 

 but it certainly lasts several months. 



Gay and Southard further found that during the period of in- 

 sensitiveness which follows a large dose the animal actually 

 contains the substance which acts as a sensitizing agent. Thus a 

 guinea-pig which had received (in divided doses) 17 c.c. of normal 

 horse serum was bled fourteen days after the last dose: 1*5 c.c. 

 of its serum was found to sensitize a normal guinea-pig, so that it 

 died in ninety minutes after an injection of normal horse serum. 

 (Rosenau and Anderson had already found that the young of 

 sensitized animals are also sensitive.) Further, Gay and Southard 

 found the sensitizing substance present in the blood of sensitized 

 animals. Thus a guinea-pig received y^g- c.c. of horse serum, 

 and after twenty-nine days was bled, and 1*5 c.c. found to sensi- 

 tize another animal. The first pig was tested and found to be 

 sensitive. 



These discoveries are sufficiently astonishing, and there appears 

 to be no satisfactory explanation for them. The period of incuba- 

 tion would suggest that we are dealing with antibodies of some 

 sort, but there is no evidence to show that the precipitins play any 

 part in the process. An animal may be highly sensitive when no 

 precipitin can be demonstrated in its serum. 



Gay and Southard think that the hypersensitiveness depends on 

 the presence of a substance which occurs in horse serum, and 

 which they distinguish by the name anaphylactin. 1 This they do 

 not consider to be the same as the toxic ingredient of the serum, 

 for this reason : a sensitized animal will not develop symptoms 

 after the injection of blood from an animal in the refractory stage, 

 though this, as we have seen, was sufficient to sensitize it. (The 

 injections were made into a vein, the sensitive animal reacting to 

 very minute doses administered by this channel.) They failed to 

 find any proof of the formation of antibodies in the animal during 

 the refractory stage. They regard the reaction as being one of 

 the cells of the sensitized animal, and as being due to a heightened 

 power of absorption of the " toxic substance " on the part of cells 

 which have been exposed for a certain period to the action of the 

 anaphylactic substance. The action of this toxic substance 

 1 Analogous to Richet's toxogenic substance. 



