MENTAL DIFFERENCE AND DISORDER. 207 



most apt to be developed. Hi-health, produced by any one 

 or more of the before-mentioned causes and they generally 

 operate in considerable combinations is favourable to the 

 production of insanity in other animals as in man, when the 

 debilitated system is exposed to the same additional, power- 

 fully exciting or depressing influences. Hl-health, in fact, 

 constitutes a very common predisposition to, or predisposing 

 cause of, mental disturbance in the lower animals. 



Horses too long in harness are liable to nervous agitation, 

 delirium, and the exhibition of mad-like actions (Houzeau) ; 

 so that overwork in them, as in other animals trained to 

 man's uses, is not only a mistake in policy, economy, and 

 humanity, but it is directly dangerous to human life. Closely 

 allied to the subject of overwork is meagre rest, want of sleep. 

 The necessity for the periodical renewal of energy mental 

 as well as bodily is quite as great among the lower animals 

 as in man ; and hence sleeplessness, especially if protracted, 

 begets the same kind of psychical and physical results. 

 Thus it is provocative of mental and bodily languor or list- 

 lessness. The Koraks, in the treatment of their teams of 

 Esquimaux dogs, show an example to many more civilised 

 peoples in their recognition of the need of ample rest and 

 sleep for hard-working animals. 



All kinds of bodily suffering or pain may produce a kind 

 of waking temporary delirium, which is but a stage towards 

 mania (Houzeau). We read of the rhinoceros, elephant, 

 reindeer, and other large animals being 'maddened with 

 pain,' be it of toothache or fracture, the bites or stings of 

 insects, or the wounds inflicted by man. The expression, so 

 frequently used in reference to our domestic or menagerie 

 animals, of being * mad with pain ' probably describes a 

 furiosity that is apt to pass into, if it be not sometimes a 

 transient, mania. 



All exhaustion of body which involves weakness of brain 

 is accompanied by, or leads to, certain kinds of nervous and 

 mental excitement. 



The nature of the diet, of the food and drink, especially 

 the former, has a very direct and marked influence on the 

 mental character of the lower animals. Thus a stimulant 



