TOXIC OR EXCITING INJECTION 31 



dosage was clear : it must be a guinea-pig sensitised 

 to the serum. 



It will be understood that while we — and others 

 with us — always limited ourselves to the subdural 

 injection of the same dose (0-25 c.c.) of the serum, it 

 was impossible to estimate the difference between 

 one serum and another. When injected in this 

 quantity all the sera, irrespective of their origin, 

 nature, or age, invariably kill the guinea-pig in a few 

 minutes. If the animal survives — and this does 

 sometimes happen — this dose never fails at the very 

 least to set up characteristic symptoms of a very 

 grave nature. 



By progressively diminishing the doses of the serum 

 we were enabled to demonstrate the fact that all sera 

 were not toxic to the same extent, but that there were 

 very marked individual differences between them. 

 In that way we hit upon the idea of determining in 

 the case of each serum its coefficient of toxicity. 



In order to form a general idea of the toxicity of 

 sera we had samples of them imported from Russia, 

 Germany, England, Switzerland, and America, and 

 after having established the titre of toxicity for each 

 one of them, we arrived at the conclusion that there 

 are sometimes very great differences between one 

 serum and another. These differences depend largely 

 on the age of the serum, but in addition there exists 

 an individual factor which depends altogether on the 

 breed of the horses, on their food-supply, and perhaps 

 on the manner in which the serum is collected. 



We can demonstrate the fact that the addition of 

 preservative fluids and antiseptics (carbolic acid, 

 trikresol, chloroform) in use in most countries fails 

 to exercise any influence on the toxicity of sera. 



Amongst the causes of toxicity, that due to the age 

 of the serum deserves the most attention. As our 

 experiments have indicated, the age of the serum no 



