544 



A MANUAL OF PHYSIOLOGY 



In all the great functions of the body we find that muscular 

 movements play an essential part. The circulation and the 

 respiration, the two functions most immediately essential to 

 life, are kept up by the contraction and relaxation of muscles. 

 The movements of the digestive canal, the regulation of the 

 blood-supply to its glands and to all parts of the body, and 

 that immense class of movements which we call voluntary, 

 are all dependent upon muscular action, which, again, is 

 indebted for its initiation, continuance, or control, to 

 impulses passing along the nerves from the nerve-centres.. 



FIG. 158. Du POIS-REVMOND'S KEY. 



FIG. 159. TIME-MARKER. 



Arrangement for marking 2 intervals. 

 D, seconds pendulum, with platinum 

 point E soldered on ; A, mercury trough, 

 into which E dips at end of its swing ; 

 B, Daniell cell ; C, electro-magnets, 

 which draw down writing-lever F when 

 the current is closed by E dipping into 

 A ; G, spring (or piece of indiarubber), 

 which raises F as soon as current is 

 broken. 



Hitherto we have not gone below the surface fact, that 

 muscular fibres have the power of contracting, either auto- 

 matically, or in response to suitable stimuli. In this chapter 

 and the two next we shall consider in detail the general 

 properties of muscle, nerve, and the other excitable tissues. 

 Lying deeper than the peculiarities of individual muscles, 

 muscular tissue has certain common properties, physical, 

 chemical, and physiological. The biceps muscle flexes the 

 arm upon the elbow, and the triceps extends it. The 

 external rectus rotates the eyeball outwards. The inter- 

 costal muscles elevate the ribs. The sphincter ani seals up 

 by a ring-like contraction the lower end of the alimentary 



