n6 The Field Naturalist's Quarter ly May 



substances have been supposed to exist from time imme- 

 morial by native tribes in various parts of the world, and 

 many curious substances have been credited with possessing 

 this antidotal power. Research in recent years has demon- 

 strated that in two ways especially can this acquired 

 immunity be conferred. One method, elaborated by Prof. 

 Sir Thomas Fraser, is by the use of bile, the secretion of the 

 liver. He showed in a series of experiments that within 

 certain limits bile had the capacity of antagonising certain 

 doses of snake-venom when injected as a mixture of both, 

 or the bile separately. The other method is by injecting 

 gradually increasing doses of venom into an animal until it 

 contains in itself the specific anti-substance which renders it 

 immune to ordinary fatal doses. This substance is contained 

 in the blood-serum, and this when injected into another 

 animal confers immunity upon the latter for a certain time. 

 Dr Andrew Wilson was of opinion that the Mongoose, from 

 long association with its snake enemies, may have developed 

 a blood-immunity in this way, and that natural selection, 

 acting in the direction of the survival of the fittest, had pro- 

 duced a species of mammal, the Mongoose, which was 

 naturally immune. That is a perfectly scientific theory, and 

 doubtless in some degree represents what has actually taken 

 place in those animals which undoubtedly possess natural 

 immunity to some diseases. Whether this has occurred in 

 the case of the Mongoose is another matter, and the balance 

 of evidence seems to prove that it is not so. 



In the first place, it has been amply proved that the 

 Mongoose often succumbs to the bite of the serpent, which, 

 of course, would not happen were it naturally immune. 

 The question then is, Why does the Mongoose not always 

 succumb ? To this there are only two possible answers. 

 One is, that the Mongoose in his encounters with the cobra 

 or other serpent is not bitten at all; in other words, that he 

 bites first, and that so effectually that the snake is put out 

 of action. The other possibility is that, having sustained 

 what would otherwise be a fatal dose of venom, the 

 Mongoose, in virtue of the special knowledge he has ob- 

 tained from instinct or experience, is able to select an 

 antidote for the venom, and thus save his life. Very de- 



