MENTAL DIFFERENCE AND DISORDER. 221 



where no real danger exists. On the other hand, nervous- 

 ness, timidity, terror, may pave the way for mania instead 

 of mere delusion. 



It would appear to be darkness that accounts ' for the 

 nervous state of terror in a wheatear (bird) at a passing 

 cloud, which, when sailing in the atmosphere above him, in- 

 duces the bird to seek shelter in the nearest hole' (Berkeley). 

 In the same way eclipses especially of the sun produce 

 fear in certain animals, causing them to seek shelter or 

 safety, while some birds make the mistake of roosting, as if 

 for the night, or they give forth their night song (Pierquin). 

 Darkness aud light, moreover, have an obvious relation to 

 ferocity or courage, and their opposites, in certain animals 

 e.g., the lion. 



Pierquin describes the effects of the variations in the 

 electrical condition of the atmosphere on the cat. A surplus 

 of electricity in the air, a state of high electrical tension, 

 produces sometimes hilarity, gaiety, noisiness, amounting 

 occasionally to a kind of joyous mania, a morbid exuberance 

 of animal spirits, especially in young animals, which are 

 characterised by greater nervous impressionability than 

 their seniors > Stormy weather, therefore, leads to sportive- 

 ness and general exalted activity, mental and bodily. Thun- 

 der, however, terrifies many animals, as it does many timid 

 children and women. But this may be less from the electrical 

 condition of the atmosphere than from the sudden darkness 

 and heavy rain, for certain animals have a great aversion to 

 rain or wet, or from the sudden, unusual, and terrifying 

 noise. In South American cattle coming thunder produces 

 excitement, amounting sometimes to madness or possession, 

 preceded by much sniffing and agitation ('Percy Anecdotes'). 



Certain colours produce a singular and rapid effect on 

 some animals, in certain cases this effect taking the form of 

 mere aversion or antipathy, but in others that of an excite- 

 ment or irritation that may amount to dangerous fury or 

 mania, or that may lead even to suicide. There is no one 

 colour that is an irritant to all colour- sensitive animals. 

 Instances are on record of mental excitement, more or less 

 intense, arising from white and black, as well as red-coloured, 



