150 MENTAL EVOLUTION IN ANIMALS. 



at the vacant air, as if pursuing something against which it 

 had an enmity." And, indeed, this peculiarity of being 

 liable to optical delusions is so usual and well marked a 

 feature in rabid dogs, that it generally constitutes the earliest 

 and most certain symptom of disease.* My friend Mr. Walter 

 Pollock sends me the following account of a Scotch terrier 

 bitch which he possessed : — " She had a curious hatred or 

 horror of anything abnormal — for instance, it was long before 

 she could tolerate the striking of a spring bell, which when 

 I first knew her was a new experience to her. She expressed 

 her dislike and seeming fear by a series of growls and barks, 

 accompanied by setting her hair up on end. She used from 

 time to time to go through exactly the same performance 

 after gazing fixedly into what seemed to be vacancy. This 

 attracted my attention, and I used to be on the look out for 

 it, but carefully avoided in any way tempting her to make 

 any display of this peculiarity. I simply watched her when- 

 ever I was alone with her. The constant repetition in these 

 circumstances of her seeming to see some enemy or portent 

 unseen by me, and giving vent to her feelings in the way 

 already described, led me to the conclusion that at these 

 times she was the victim of optical illusion of some kind. I 

 could, as I have already hinted, produce the same effect upon 

 her by doing some unexpected and irrational thing, until she 

 had become accustomed to this kind of experiment But 

 after this the seeing, as it seemed to be, of some sort of 

 phantom remained unabated. I had no opportunity of dis- 

 cerning whether the phenomena occurred at any regular 

 intervals, or whether they were more frequent after sleep 

 than at other times." 



Pierquin describes a female ape which had a sun-stroke, 

 and afterwards use to become terror-struck by delusions of 

 some kind. She also used to snap at imaginary objects, and 

 " acted as if she had been watching and catching at insects 

 on the wing."f 



It seems needless for our present purpose to give more 

 evidence on the fact of animals being subject to delusions, 

 and so I shall pass on to the third class of facts on which I 

 rely as evidence that animals present Imagination of what I 

 have called the third order. This class of facts consists of 



* See Youat, On the Dog, under Rabies. 



t Trade de la Folie des Animaux, c$t\, tome i, p. 93. 



