34 2 The Naturalist in La Plata. 



tagious, like fear, that communicates itself, quick 

 as lightning, from one to another until all are in a 

 panic, and like the joyous emotion that impels the 

 members of a herd or flock to rush simultaneously 

 into play. 



Now, it is a pretty familiar fact that animals acting 

 instinctively, as well as men acting intelligently, 

 have at times their delusions and their illusions, 

 and see things falsely, and are moved to action by a 

 false stimulus to their own disadvantage. When 

 the individuals of a herd or family are excited to a 

 sudden deadly rage by the distressed cries of one 

 of their fellows, or by the sight of its bleeding 

 wounds and the smell of its blood, or when they see 

 it frantically struggling on the ground, or in the 

 cleft of a tree or rock, as if in the clutches of a 

 powerful enemy, they do not turn on it to kill but 

 to rescue it. 



In whatever way the rescuing instinct may have 

 risen, whether simply through natural selection or, 

 as is more probable, through an intelligent habit 

 becoming fixed and hereditary, its effectiveness 

 depends altogether on the emotion of overmastering 

 rage excited in the animal — rage against a tangible 

 visible enemy, or invisible, and excited by the cries 

 or struggles of a suffering companion ; clearly, then, 

 it could not provide against the occasional rare 

 accidents that animals meet with, which causes them 

 to act precisely in the way they do when seized or 

 struck down by an enemy. An illusion is the result 

 of the emotion similar to the illusion produced by 

 vivid expectation in ourselves, which has caused 

 many a man to see in a friend and companion the 



