176 THE BOOK OF A NATURALIST 
It is not the same in the western prairies of 
North America. Venomous serpents are relatively 
more abundant there, and grow larger, and their 
bite is more dangerous. The horse learns to fear 
them, especially the rattlesnake, on account of 
its greater power, its sluggish habits and warning 
faculties. The sound of the rattle calls up the 
familiar ophidian image to his mind; and when 
the rattle has failed to sound, the smell will often 
serve as a warning; which is not strange when we 
consider that even man, with his feeble olfactory 
sense, is sometimes able to discover the presence 
of a rattlesnake, even at a distance of several feet, 
by means of its powerful musky effluvium. The 
snake-eating savages of Queensland track their 
game by the slight scent it leaves on the ground 
in travelling, which is quite imperceptible to 
Europeans. In the same way the horse is said to 
smell wolves, and to exhibit instinctive terror when 
they are still at a distance and invisible. The 
terror is not instinctive. The horses of the white 
settlers on some frontier lands, exposed to frequent 
attacks from savages, smell the coming enemy, and 
fly in panic before he makes his appearance; yet 
when horses are taken from the savages and used 
by the whites, these too after a time learn to 
show terror at the smell of their former masters. 
Their terror is derived from the horses of the 
whites. The hunter Selous, as a result of ten years 
of observation while engaged in the pursuit of big 
game in the heart of Africa, affirms that the horse 
