392 INFECTION AND RESISTANCE 



toneal sensitization of guinea pigs with constant quantities of titrated 

 precipitating serum. Twenty-four hours later intravenous test with 

 diminishing amounts of specific antigen. 2. Intraperitoneal sensi- 

 tization with diminishing quantities of the titrated precipitating 

 serum, and 24 hours later intravenous tests with constant amounts 

 of antigen. 



In this way they showed that there was a direct relationship be- 

 tween the power of a serum to convey anaphylaxis passively and its 

 contents of precipitins. We may elucidate this by an example from 

 their work. They possessed a rabbit serum which gave precipitation 

 with sheep, goat, beef, pig, human, and horse sera, but not with 

 chicken serum. The precipitation titre of this serum for the sera 

 mentioned varied from 1 in 20,000 in the case of sheep and goat 

 sera, to 1 in 100 in the cases of the human and horse sera. When 

 guinea pigs were injected intraperitoneally with 1 c. c. of this serum, 

 and after 24 hours were intravenously injected with the various sera 

 mentioned above, in decreasing quantities, the sera which were pre- 

 cipitated in the highest dilutions gave anaphylactic shock in the 

 smallest quantities. Those sera for which no precipitin or little had 

 been present in the antiserum gave little or no reaction by this 

 method even where considerable quantities were used. Thus in ani- 

 mals prepared by 1 c. c. of this antiserum, the sheep serum (precipi- 

 tated in dilutions of 1 in 20,000) caused death when injected in 

 doses of 0.006 c. c., whereas horse serum (which was precipitated 

 only in concentration of 1 to 100) gave slight symptoms only when 

 2 c. c. were employed for reinjection and chicken serum (non- 

 precipitable by the antiserum) gave no reaction in similar doses. 



In this, then, we have a definite quantitative analysis which 

 proves that the power to sensitize passively is in* direct relation to the 

 antibodies against the protein present in the sensitizing serum. 

 Whether or not this means the precipitins particularly we will con- 

 sider in a later section. 



We are now prepared to follow individually the development of 

 those theories in which the anaphylactic mechanism was looked upon 

 purely as the result of the union of an antigen with its antibody. 



The conception which gradually grew out of the antigen-antibody 

 mechanism of anaphylaxis was the following: When a specific an- 

 tigen meets its antibody the reaction between them gives rise to a 

 toxic product, and this causes the characteristic symptoms. A simi- 

 lar idea, it will be remembered, is found in the original endotoxin 

 theory of Pfeiffer. According to this, the action of the specific 

 lysin liberated from bacteria a preformed poison, the endotoxin. 

 In 1902 Weichhardt, 19 bearing this conception in mind, subjected 

 syncytial protein of rabbit placenta to the action of specific antisera 

 and obtained substances toxic for normal rabbits. 



19 Weichhardt. Deutsche med. Woch., 1902, p. 624. 



