JACKALS, ETC. 279 



that both of these factors come into play to produce 

 the result, or, in other words, that in normal circum- 

 stances mature mungooses do possess an exceptional 

 immunity from the results of encounters with 

 venomous colubrine and viperine snakes, partly 

 owing to the presence of constitutional peculiarity, 

 and partly because they are seldom exposed to the 

 action of large doses of venom, due to their wonder- 

 ful activity and skill in dealing with the snakes. It 

 remains, however, to be determined how far the 

 constitutional immunity is of an hereditary or an 

 acquired nature. Experimental research has clearly 

 proved that a very high degree of immunity is 

 evolved in animals who have been treated with 

 progressively increased doses of venom, ranging 

 upwards from normally sublethal amounts through 

 a series of larger and larger ones. But any animals 

 like mungooses, who are frequently engaged in 

 conflicts with deadly snakes, must almost certainly 

 be practically exposed to such treatment, and under 

 these circumstances, it is only natural that adult 

 mungooses who have grown up at liberty should 

 possess a certain degree of immunity. What is 

 wanting to complete our information on the subject 

 is a series of experiments on animals which have been 

 born and reared in captivity under conditions pre- 

 cluding the possibility of encounter with venomous 

 snakes. Should they show any immunity, the latter 

 must be of an hereditary origin, and would apparently 



