1907.] on Nerve as a Master of Musde. 618 



has occurred, aud has done the appropriate thing. A candle may be 

 brought into the room and its hght reach the face of the child. That 

 is a change in the outside world in relation to the child. The familiar 

 fact is that the child's head turns from the light. It sees no light, 

 but reflex action averts its face. Or, turning to other forms of hfe, 

 take a fish quiet in its aquarium. A worm is dropped into the water, 

 and the disturbance of the water reaches the surface of the fish. The 

 fish turns and seizes the morsel. Such a reaction on the part of such 

 a creature is probably wholly reflex! 



The point for us here is, that the changes in the outside world 

 which act as stimuli bring about appropriate readjustments of the body 

 to the external world, and that in doing so the instruments of readjust- 

 ment are the skeletal muscles, worked by the nervous system. The 

 child's heart goes on beating, whether the child's foot lies quiet or is 

 moved, whether its face hes this way or lies that ; the fish's heart 

 whether the animal's skin was stimulated by fresh commotion in the 

 water, or was not. But with the skeletal muscles it was different. 

 Flexor muscles of the leg, that were relaxed, are by the touch to the 

 foot thrown into action ; muscles which lay relaxed were, when the 

 light came, caused to contract turning the head away. Muscles of the 

 fish that were inactive were thrown into activity by the new commo- 

 tion in the water. It is these skeletal muscles, therefore, that the 

 daily thousand changes of the external world so repeatedly and con- 

 stantly affect in this way or that, and in reflex action it is always 

 the receptors and the nervous system which impel them to react. 

 And the result is to readjust advantageously to the animal its rela- 

 tion to the altering external world. Hence these muscles are called 

 the muscles of external relation. So prominent are these muscles in 

 the everyday work of life that they are the muscles of ordinary parlance. 

 The man in the street is hardly aware that he has in his body any 

 other muscles. And these muscles are, through the nervous system, 

 driven by the external world. The world outside drives them by 

 acting on the receptors. It is not surprising, therefore, that this 

 little muscle, removed from the body, and therefore separated from 

 the nervous system and all its receptors, remains, although still living 

 and able to contract, as functionally inactive — for contraction is its 

 function and it does not contract — as if it were already dead. 



Xow this muscle, when in the body, was the servant of a thousand 

 masters. It had to contribute to a thousand acts. In a certain sense, 

 it, hke the heart, had to do for them all but one thing, inasmuch as 

 it had to pull the limb in one certain direction, iind yet its task is 

 a very varied one. It has to pull the limb sometimes far, sometimes 

 very slightly, or through all intermediate grades. It has to pull it 

 strongly against great resistance, or weakly, and with all intermediate 

 grades of intensity. We may suppose that in the course of evolu- 

 tion it had become adapted to this scope of purpose. 



And indeed we find it so. Unlike the heart muscle this muscle when 



