1896.] on Immunisation against Serpents' Venom. 117 



venom, even fifteen times larger tlian the minimum-letlial, may be 

 administered without producing more than an inconsiderable degree 

 of local destructive effect. 



Experiments have also been made by which it has been demon- 

 strated that when an animal has acquired a resistant power over the 

 minimum-lethal dose of one venom, that animal is also able success- 

 fully to resist the lethal action of a dose above the minimum-lethal 

 of other venoms. To a rabbit protected against cobra venom, a dose 

 above the minimum-lethal of Sepedon venom has been administered ; 

 to rabbits protected against Crotalus venom, doses above the mini- 

 mum-lethal of Diamantina and of cobra venoms have been given ; to 

 rabbits protected against the Diamantina venom, doses above the 

 minimum-lethal of Crotalus and Sepedon venoms have been given ; 

 and in each case the animal has recovered, and but few symptoms of 

 injury were produced. At the same time, in other experiments, 

 indications were obtained that animals protected against a given 

 venom are capable of resisting the toxic effect of that venom more 

 effectually than the toxic effect of other venoms. 



The experiments have not yet proceeded sufficiently far to show 

 for what length of time the protection conferred by any final lethal 

 dose may last. It has been discovered, however, that protection lasts 

 for at least a considerable period of time, even when the last protec- 

 tive dose has not been a large one. For example, to a rabbit which 

 had last received four times the minimum-lethal dose of cobra venom, 

 twice the minimum-lethal dose was administered thirty-four days 

 subsequently ; while to another rabbit, which had last received twice 

 the minimum-lethal dose of Crotalus venom, the same dose of this 

 venom was administered twenty days subsequently, and in each case 

 the second dose failed to produce any toxic symptom. 



Having thus succeeded in producing a high degree of protection 

 in animals against the toxic effects of serpents' venom, the blood-serum 

 of these animals was, in the next place, collected for the purpose of 

 testing its antidotal properties. In this portion of the investigation, 

 the method followed was essentially the same as that described in a 

 communication made by me to the Eoyal Society of Edinburgh in 

 1871, on " The Antagonism between the Actions of Physostigma and 

 Atropia," as it appeared to be the most direct method for obtaining 

 accurate knowledge of the value of an antidote. 



A few preliminary experiments were, however, early made with 

 the serum of animals in whom the protection had not been carried to 

 a high degree, and they were sufficient to show that antidotal proper- 

 ties are possessed even by this serum. It soon became apparent that 

 in order to obtain some reasonable approximation to constancy in the 

 conditions of the experiments, it was necessary that the serum should 

 be in such a state that it would remain unchanged during at least 

 several weeks. It was found that this could be insured, without any 

 appreciable loss of antidotal power, by drying the freshly-separated 

 serum in the receiver of an air-pump over sulphuric acid. 



