VACCINATING INJECTION 51 



next by a regular interval of six days, and each con- 

 sisting of a massive dose of serum (5 c.c). After 

 having given three or four inoculations in this way, 

 they again waited six days, and then proceeded to 

 the test injection. As this test did not lead to the 

 death of the animal, they believed that they had 

 effected active vaccination against the toxin of the 

 serum. 



In the same manner we ourselves made our first 

 attempts at obtaining passive immunity. In order 

 passively to immunise against anaphylactic symp- 

 toms — that is to say, against the supposed toxin of 

 horse serum — we began by inoculating guinea-pigs 

 with a series of massive injections of horse serum; 

 and when we considered the animals to be well 

 immunised, we bled them, and mixed their sera 

 with the supposed toxic horse serum in the hope of 

 neutralising its effect. 



Our hope was not realised, for a very good reason, 

 as we ultimately understood. The horse serum 

 remained quite as toxic after this operation as before. 

 It might, strictly speaking, be thought that the 

 poison contained in the serum was one of those which 

 did not yield antibodies easily. But, in reflecting on 

 this, we had our doubts. After all, we said to our- 

 selves, perhaps a toxin does not exist in horse serum,^ 

 as our predecessors Rosenau, Anderson, and Otto 

 have thought. Even admitting that it does exist,, 

 why should we apply to anaphylaxis ideas borrowed 

 from immunity, especially those relating to active or 

 passive vaccinations ? 



Our doubts assumed a more tangible form when, 

 from experience, we saw that to confer immunity 

 against anaphylaxis one injection only of serum was 

 needed, and not a whole series of separate injections, 

 as in the method of Rosenau and Anderson, or of 

 Otto. Finally, when we discovered with surprise 



