458 BIOLOGICAL PHYSICS 



and their vascular and circulatory textures, are mechanically 

 compressed, and partially emptied, the " tears then spring- 

 ing into the eyes," and down into the nostrils, and the 

 saliva " welling" into the mouth. 



This act then becomes in our estimation, when viewed 

 in the light of its probable functional value, one of the 

 very greatest importance in its relation to our physical, 

 and, it may be to some extent, to our mental comfort and 

 well-being. And here, perhaps, it may be well to express 

 our surmise that there is a difference in nature and 

 intensity between the night and the morning yawns, the 

 former preceding and ushering in sleep, and the latter 

 completing the act of awakening, and that, in a manner, 

 the yawn acts as a switch in the economy of inhibition. 



When exhausted, wearied, bored, or suffering: from 



O 



ennui, and sorely needing rest, the handle, so to speak, 

 of the inhibitory mechanism is seized by the needful 

 yawn, and held, until finally it falls from its grasp, as 

 sleep asserts its sway. After which, sleep's sway is 

 enjoyed for a season, or until nature's requirements 

 have been met, when the act of awaking once more 

 instigates the yawn to " turn the inhibitor," and the 

 more vigorously its powers are exerted the more, in 

 proportion, is felt the " sense of refreshment " from 

 the preceding slumbers ; when again the eyes are bathed 

 with lubricating moisture the nostrils are flushed with 

 the superabundant lachrymal flood, and the mouth and 

 fauces are irrigated by the expressed saliva, and tonsillo- 

 pharyngeal mucoid excretion. Thus the machinery of 

 at least three of the senses sight, smell, and taste, and 

 probably hearing and touch is refitted for the comfortable 

 and more efficient performance of duty. Therefore, we 

 say, let the yawn have complete local and general control 

 when the exigencies of etiquette will allow, and if these 

 latter forbid, then the very first opportunity should be 

 seized of gratifying waiting nature. We refrain, however, 

 at present from entering on the subject of the therapeutic 

 value of this essential and natural act, and the description 

 of a regulated system of yawning and stretching exercises 

 the elaboration of which should be fraught with great 

 physiological benefits. 



