32 ANAPHYLAXIS AND ANTI-ANAPHYLAXIS 



longer intervenes as a factor when six weeks or two 

 months have elapsed since the venesection. After 

 that individual toxicity alone has to be reckoned with. 

 We have estabhshed it as a fact that in the great 

 majority of cases the lethal dose for the sensitised 

 guinea-pig is from 0-084 to 0-125 c.c. of serum. We 

 have, however, seen sera destroying guinea-pigs, in 

 intracerebral or intravenous injections, when the dose 

 has been 0-0625 c.c; and, moreover, other sera — ^not 

 many, it is true — which proved to be exceedingly 

 toxic in doses as small as 0-0 1 5 to 0-032 c.c, and which 

 set up anaphylactic symptoms in still weaker doses 

 {e.g., 0-0063 c.c). 



The causes of the marked toxicity of certain sera, 

 independent of their age, still elude us. The fact of 

 its occurrence is useful to know; and we shall be on 

 our guard against it. 



On the other hand, the toxicity which is due to 

 the age of the serum lends itself to more accurate 

 analysis. This toxicity has been studied in horses 

 belonging to the Pasteur Institute, all living under 

 the same conditions, receiving the same kind of food, 

 and being treated in the same way. 



In spite of this equality of conditions, we found 

 from time to time instances of sera exhibiting a some- 

 what unequal toxicity. If the sera be examined at 

 various intervals of time after venesection the findings 

 are as follows : At the outset the toxicity of all the 

 sera is almost equal ; after this it decreases at a fairly 

 regular rate. The serum is very toxic on the first 

 day — that is, the day of the venesection (lethal dose 

 ==0-032 c.c), but it rapidly loses its toxicity during 

 the next ten days. As the eleventh day approaches, 

 the toxicity is almost diminished by half (lethal 

 dose=o-o63 c.c). It continues very slowly to de- 

 crease during the next thirty or forty days, and 

 when injected in the dose which previously has been 



