76 ANAPHYLAXIS AND ANTI-ANAPHYLAXIS 



desensitisation was the fact that sensitised guinea- 

 pigs, when once rendered anti -anaphylactic, could 

 be submitted to a fresh sensitisation. Weil and 

 Coca have taken up the same idea, investing it with 

 a quasi-mathematical expression. They likewise ex- 

 perimented with guinea-pigs which had already been 

 sensitised, and were then at a much later date 

 rendered anti-anaphylactic by one of our processes. 

 They put the following question: Are these guinea- 

 pigs to be considered as having reverted to their 

 former state ? In order to ascertain this, they 

 sensitised them passively by means of an antiserum.^ 



The experiment shewed that to effect this pro- 

 cedure it was necessary to employ the same quantity 

 of antiserum as one would have to employ in the 

 case of sensitising fresh guinea-pigs. In other words, 

 the animals rendered anti-anaphylactic behave at 

 the time of passive resensitisation exactly like control 

 animals that have never undergone any injection. 



Weil and Coca have thus been led to conclude that 

 the term which best expresses the mechanism of 

 anti-anaphylaxis is that of " desensitisation " which 

 we proposed in 1907. 



Upon setting out with this conception of anti- 

 anaphylaxis, we learn what should guide the practi- 

 tioner in his choice of dose or vaccinating doses. 



The anaphylactic state being due to the presence 

 of specific antibody or sensibilisin, the duty of the 

 physician is to neutralise it as much as possible by 

 the addition of the maximum of antigen (the latter 

 is represented in the majority of cases by horse 

 serum). 



If for the purpose of vaccine a very slight quantity 

 of antigen (horse serum) be added, the end is only 

 partly attained: a little antigen neutralises a little 



^ For the description of the technique of passive sensitisation^ 

 see Chapter III. 



