PAIN, LAUGHTER AND WEEPING 327 



the brain by blocking the field of operation with local 

 anesthesia, the brain threshold is not lowered, and there 

 is consequently little or no postoperative pain. 



There is a close resemblance between the phenomena 

 of pain habit, of education, of physical training and 

 of love and hate. In education, in pain habit, in all 

 emotional relations, a low brain threshold is established 

 which facilitates the reception of specific stimuli. All 

 these processes are motor acts or are symbolic of 

 motor acts. We may be trained to perceive mis- 

 fortune and pain as readily as we are trained to per- 

 ceive mathematical formulae and moral precepts. 



Laughter and Weeping 



Much of the real nature of laughter and weeping, 

 as of pain, is revealed by an examination of their dis- 

 tribution ; that is, of the character of individuals 

 among whom they are common, and of the situations 

 to which they are incident. Laughter is an involuntary 

 rhythmic contraction of certain respiratory muscles, 

 accompanied usually by certain sounds. The motor 

 act involves the respiratory apparatus primarily, but if 

 the act is intense, it may involve not only the muscles 

 of respiration, but also most of the other muscles of the 

 body. There are many degrees of laughter, varying 

 from a mere brightening of the eyes and a fleeting 

 smile to intense hysterical and convulsive outbursts. 

 From intense or prolonged laughter, even exhaustion 

 may result. 



Laughter is sometimes accompanied by the forma- 

 ion of tears and in many instances, in children espe- 

 cially, laughing and weeping are readily interchanged. 



