PAIN, LAUGHTER AND WEEPING 321 



beneficent and important purpose. The body, stricken 

 by acute infection or poisoned by auto-intoxication, 

 needs to rest and to fast ; hence the entire muscular 

 system obeys the command of this single pain, located 

 in the controlling organ of the body, and muscular 

 relaxation follows. 



Strange and yet intelligible, in view of this concep- 

 tion, is the fact that, although a headache may be 

 induced by even a slight auto-intoxication, an abscess 

 may exist in the brain itself without causing pain. 

 Inhibition of muscular action is a protection in one 

 case ; in the other it is useless. In like manner this 

 principle may explain the acute pain that is present 

 when an obliterative endarteritis is threatening a leg 

 with anemic gangrene, or when one lies too long in 

 the same position on a hard bed so that injury from 

 local anemia threatens. But when the obliterative 

 endarteritis threatens anemia of the brain, or when an 

 embolism or thrombosis has produced anemia of the 

 brain, there may be no pain, for muscular action, which 

 in the former instance would be a protective response, 

 in the latter would be of no use. 



A most striking instance of the protective nature of 

 pain is found in the phenomena of peritonitis. 

 Through the law of natural selection, the peritoneum, 

 in its relation to vast fields of possible infection, has 

 become wonderfully endowed with mechanisms for 

 resisting and overcoming infection. If the focus can 

 be localized, almost any infection in the peritoneum can 

 be overcome. This localization is accomplished by 

 holding the muscular intestinal walls still and rigid 

 against a large volume of gas, and by quickly throwing 



