CHAPTER VII 

 THE PROPERTIES OF MUSCULAR TISSUE 



Contractility. The characteristic physiological property of 

 muscular tissue, and that for which it is employed in the Body, is 

 the faculty possessed by its fibers of shortening forcibly under 

 certain circumstances. The direction in which this shortening 

 occurs is always that of the long axis of the fiber in both plain and 

 striped muscles, and it is accompanied by an almost equivalent 

 thickening in other diameters, so that when a muscle contracts it 

 does not shrivel up or diminish its bulk in any appreciable way; it 

 simply changes its form. When a muscle contracts it also be- 

 comes harder and more rigid, especially if it has to overcome any 

 resistance. This and the change of form can be well felt by placing 

 the fingers of one hand over the biceps muscle lying in front of the 

 humerus, of the other arm. When the muscle is contracted so as 

 to bend the elbow it can be felt to swell out and harden as it 

 shortens. Every schoolboy knows that when he appeals to an- 

 other to " feel his muscle " he contracts the latter so as to make it 

 thicker and apparently more massive as well as harder. In statues 

 the prominences on the surface indicating the muscles beneath the 

 skin are made very conspicuous when violent effort is represented, 

 so as to indicate that the muscles are in vigorous action. In a 

 muscular fiber we find no longer the slow, irregular, and indefinite 

 changes of form seen in amreboid slightly differentiated cells; 

 they are replaced by a precise, rapid and definite change of form. 

 Muscular tissue represents a group of cells in the bodily com- 

 munity which have taken up the, one special duty of executing 

 changes of form, and in proportion as these cells have fewer other 

 things to do, they do that one better. This contractility of the 

 muscular fibers may be briefly described as a passage from the 

 state of rest, in which the fibers are long and narrow, into the 

 state of activity, in which they are shorter and thicker: this 

 change is made with considerable force, and thus the muscles 

 move parts attached to their tendons. When the state of activity 



87 



