382 THE POPULAR SCIENCE MONTHLY. 



recorded in bold characters, in another may leave scarcely a visi- 

 ble mark ; and it is obvious that a lean face will betray the story 

 of emotional experience more readily than one covered with a 

 mask of fat and smooth skin. 



If we look at an anatomical representation of the human face 

 with its integument removed, we see at once that the various 

 groups of muscles are generally so arranged as to balance one 

 another. Thus there is one set of muscles for opening the eyes or 

 the lips, and another set for closing them ; one group raises and 

 another depresses the angles of the mouth, and so on. All these 

 muscles, even when the features are quiescent, maintain a certain 

 tone ; for it is found that if one part of the face is paralyzed, the 

 sound muscles near it draw it toward them and retain it there 

 even when they are at rest. If one of the muscles or groups is 

 stronger in proportion than its opponents, it will cause a marked 

 change of expression, as is plainly seen in partial paralysis. It 

 is a familiar fact that all muscles become larger and stronger 

 through exercise ; but the reason why they so increase is not such 

 a simple matter. The vitality of muscular, and indeed of all other 

 living tissue, is strangely under the influence of the nervous system. 

 If the nerves which supply a limb are totally destroyed, it shrinks 

 with extraordinary rapidity, although the main blood supply re- 

 mains perfect. At the same time a limb may be paralyzed as to 

 motion and yet undergo but little wasting, because certain nerve 

 fibers (called trophic, because they have to do with nutrition) are 

 left intact. In bedridden patients, again, in spite of a total want 

 of exercise, the muscles often do not shrink in any great degree. 

 Hence we see that nervous currents or impulses may influence the 

 growth of a muscle apart from actual exercise. 



Let us take an instance, the too visible results of which every 

 one is familiar with. Persons who squint (with certain exceptions 

 I need not here specify) are always "far-sighted" that is, the 

 convex lens of that marvelous living camera, the eye, is not quite 

 convex enough ; and in consequence its focus is too long to per- 

 mit rays from a near object to form a clear image on the retina. 

 If the retina could be pushed back away from the lens the diffi- 

 culty would be overcome ; but we can not, as in the case of an 

 opera glass or a photographic apparatus, lengthen the space be- 

 tween the lens and the spot upon which the image is to be pro- 

 jected to any great extent, so Nature has provided a focusing 

 apparatus in the crystalline lens itself. By a muscular effort the 

 elastic lens can be made more convex, and in this way the focus is 

 shortened to the required length. In long-sighted or flat-lensed 

 persons this is constantly being done when they are reading or 

 looking at some near object. 



Now, it so happens that one of the little muscles which move 



