132 



STUDIES IN ADVANCED PHYSIOLOGY. 



to atrophy. There is in the body a nervous arrangement 

 by which the blood-vessels leading to the muscle are at 

 once enlarged as soon as that muscle is called into action. 

 These are the dilator nerves, which will be treated in detail 

 in the chapter on circulation. By this arrangement a work- 

 ing muscle receives an extra amount of nourishment, and 

 of oxygen, to carry on its added work. The vitality of a 

 muscle seems also to be dependent upon its connection with 

 the nervous system. A muscle with its nerve cut begins to 

 atrophy at once. The fibres become shrunken and turbid, 

 and soon lose their power of contractility. This explains 

 why in persons suffering with paralysis the muscles begin 

 so rapidly to shrink and weaken. 



Electrical Phenomena in Muscles. 



When a muscle is cut out of the body and tested with a 

 galvanometer there may be demonstrated running through 

 its substance small currents of electricity. The central or 

 uncut portion of the muscle seems to be positive with refer- 

 ence to the cut ends. Thus, if the wires be placed one on 

 the center of the muscle and the other at the end, a current 

 runs through the wires from the central portion toward the 

 ends, and of course in the muscle, to complete the circuit, 

 from the ends toward the center. These currents have been 



Fig. 68. DIAGRAM TO SHOW THE DIRECTION OF THE MUSCLE CURRENTS IN AN- EXCISED 



MUSCLE. 



e,f, central positive portion; o, c, b, d, cut negative ends. The lines with arrows in- 

 dicate the direction a current would take between the points touched. In lines 6, 7, 8, no 

 current appears for obvious reasons. 



