258 SCIENTIFIC ILLUSTRATIONS [Pan 



danger in such 'wounds, they never cut themselves without an 

 expression of pain. u. 



Excessive Pain Terminates in its Contrary. 



It appears that bodily pain, when excessive, generally termi- 

 nates in pleasure of a nature and kind just the reverse of that 

 which causes the nervous exhaustion. Thus we are informed 

 that Theodosius, a youthful confessor, was put to such exquisite 

 torture for singing a psalm that he hardly escaped with his life ; 

 but being asked how he could endure such extreme torment, he 

 said, " At first I felt some pain, but afterwards there stood by 

 me a beautiful young man who wiped away my sweat, and so 

 refreshed me with cold water that I was delighted, and grieved 

 only at being let down from the engine." These effects of ner- 

 vous exhaustion may be illustrated by reference to those experi- 

 ments on the effects of light upon the retina, first mentioned by 

 Darwin in his Zoonomia. It is remarkable that the contrary 

 colour is produced when the sight is fatigued ; thus if we look 

 with a fixed stare at a bright-green figure until a little wearied, 

 and then look on a white surface, we shall see a red figure. If, 

 however, we continue to look at the red until the nerve is 

 thoroughly exhausted, we shall see green. The direct sunshine 

 quickly exhausts the optic nerve-power, and by looking on it we 

 become for a time quite blind. It is probable that every part 

 of the nervous system is subject to the same law or mode of 

 action, and the brain under mental excitement, as well as physi- 

 cal, is apt to take a contrary condition, by which ideas are sug- 

 gested to the mind the very reverse of those which exhausted 

 the attention. u. 



The PerH of Panic. 



The bison is found only in the great prairies of the American 

 continent. When he is hunted he will frequently turn upon 

 his adversary, and in speed he can outstrip the swiftest horse. 

 He finds a formidable enemy in the white wolf. Hunting in 

 packs of one or two hundred, the latter fling themselves upon 

 two or three solitary bisons, and surrounding them, worry the 

 huge brutes to death. The bisons, when they catch sight of 



