198 BACTERIA IN DAILY LIFE 



symptoms which in a much more modified degree 

 characterise the injection of heated eel serum into 

 animals. This heated eel serum, which we have 

 seen is deprived of the objectionable characteristics 

 of ordinary eel serum, produces but very transitory 

 symptoms in animals, occasioning some degree of 

 somnolence, and now and again a reduction in 

 temperature, a condition from which, however, 

 the animals rapidly recover in from two to three 

 hours. Animals, however, treated with this heated 

 eel serum acquire a power of resisting the lethal 

 action of unheated or ordinary eel serum, and this 

 artificially induced condition of immunity con- 

 tinues for about three days after the completion 

 of the treatment. 



The protective properties of this heated serum 

 are not restricted to animals subsequently in- 

 oculated with eel serum, but are extended also 

 to animals which afterwards receive, injections of 

 viper serum ; but of much greater interest and 

 importance is the remarkable fact that heated eel 

 serum, as well as weak doses of the latter not 

 heated but diluted with water, are capable of 

 protecting animals from the fatal consequences 

 of the far more potent viper venom. 



It is interesting to note that, although diluted 

 eel serum can protect an animal from so deadly 

 a poison as viper venom, the serum of vipers is 



