PAIN, LAUGHTER AND WEEPING 335 



laughter must not seriously interfere with any other 

 function. Were laughter expressed with the hands 

 only, arboreal man might have fallen from the tree; 

 and if expressed by the feet, our equilibrium might be 

 lost. Laughter, therefore, is expressed by means of a 

 group of powerful muscles which can be spared easily 

 without seriously interfering with the maintenance 

 of posture or any other function. In order that the 

 products of excitation may be quickly and completely 

 consumed, the powerful group of expiratory muscles 

 must have some resistance against which they can 

 exert themselves strongly and at the same time pro- 

 vide for" adequate respiratoiy exchange. The inter- 

 mittent closure of the epiglottis serves this purpose 

 admirably, just as a horizontal bar affords the resist- 

 ance against which the muscles of the athlete may be 

 exercised. 



Weeping, like laughter, is a part of the reaction to a 

 stimulation to some form of motor activity, which may 

 or may not be performed. (Fig. 82.) Take the case of 

 a mother anxiously watching the course of a serious 

 illness in her child. If, in caring for it, she is stimu- 

 lated to the utmost to perform motor acts, she will 

 continue in a state of motor tenseness until one of 



. V } . 



two events occurs recovery or death. If. relief be 



r >V* 



sudden, as in the crisis of pneumonia, and the mother 

 is not exhausted, she will easily laugh. If tired, she 

 may cry. If death occur, however, the stimulus to 

 motor activity is suddenly withdrawn and she cries 

 aloud and may perform many motor acts as a result 

 of the stimulation to motor activity which is no longer 

 needed for the physical care of her child. 



