174 THE BOOK OF A NATURALIST 



last being the fear of an enemy which the young 

 learn from their parents or other adults they 

 associate with. Fear is contagious ; the alarm of 

 the adults communicates itself to the young, with 

 the result that the object that excited it remains 

 thereafter one of terror. Not only in this matter 

 of snakes and monkeys, but with regard to other 

 creatures, Darwin lays it down that in the higher 

 vertebrates the habit of fear of any particular 

 enemy quickly becomes instinctive ; and this false 

 inference has been accepted without question by 

 Herbert Spencer, who was obliged to study animal 

 habits in books, and was consequently to some 

 extent at the mercy of those who wrote them. 



It is frequently stated in narratives of travel 

 in the less settled portions of North America that 

 all domestic animals, excepting the pig, have an 

 instinctive dread of the rattlesnake ; that they 

 know its whirring sound, and are also able to smell 

 it at some distance, and instantly come to a dead 

 halt, trembling with agitation. The fear is a fact ; 

 but why instinctive ? Some time ago, while reading 

 over again a very delightful book of travels, I 

 came to a passage descriptive of the acute sense 

 of smell and sagacity of the native horse ; and the 

 writer, as an instance in point, related that fre- 

 quently, when riding at a swift pace across country 

 on a dark night, over ground made dangerous by 

 numerous concealed burrows, his beast had swerved 

 aside suddenly, as if he had trod on a snake. His 

 sense of smell had warned him in time of some 



