$6 TOXINS AND ANTITOXINS. 



serum confers upon them an immunity against 

 venom which lasts for some time. 



These venoms, like the microbial toxins, possess 

 but slight toxicity when absorbed via the stomach. 

 Fraser, utilizing a method previously advocated, 

 succeeded, by following this method, in vaccinating 

 against serpent-venom by causing the absorption 

 by animals of constantly increasing doses of venom. 



It was thus possible to make the animals with- 

 stand doses a thousand times greater than the 

 ordinary lethal dose; the blood and serums of 

 these animals at this point possessed immunizing 

 properties, and this property passed by heredity 

 to the offspring, to which it is transmitted by 

 the blood itself, and by the milk during feeding. 



Along with these resemblances between the 

 venoms and toxins, attention must be called to a 

 very important difference. As we have already 

 seen, the action of the toxins on the organism is 

 always preceded by a certain period of incubation; 

 the action of the venoms, on the contrary, is almost 

 instantaneous, and in this respect they behave like 

 chemical agents' and alkaloidal toxins. 



If the venoms are preserved in a moist condition, 

 they change because they undergo putrefaction, 

 which is generally the case with all diastatic sub- 

 stances, and particularly the toxins. 



It is interesting to note that animals which have 

 been bitten by a venomous serpent, but which, 



