CHAPTER II. 



THE MUSCULAR MOTOR AND ALIMENTATION. 



83. (i) The Muscular Motor. The motor, in the human body, 

 is the muscle, and the force is that of contraction. 



Nervous excitement, from the motor point of view, is the 

 origin of muscular contraction, and an indefinite relation of 

 cause and effect exists between nervous and muscular movement. 

 The contraction is rapid and sudden, so that the excitement of 

 the nerve is like the priming of an explosive. When the con- 

 traction equilibrises a weight without displacing it, (static effort) 

 or moves it (work), tht muscle becomes heated, its temperature 

 rising slightly above the normal temperature and a quantity of 

 heat greater than that which is evolved in the state of repose 

 (relaxed muscle) is produced. Thus the muscle functions like a 

 heat engine. Its fuel will be considered later ( 106). 



A sustained muscular contraction is compounded of several 

 impulses. If an extremity ot a muscle is fixed at R, and the other 

 end is attached to an indicating style, AO jointed to the point O, 

 and whose point rubs on a moving surface covered with smoke 

 blackened paper, then by an electric stimulus to the ntrve N, the 



trace ACD is produced (fig. 

 120). The duration of ACD, 

 read on the line T of the 

 time is from 12 to 16 hun- 

 dredthsof a second in adults. 

 'L It is gi eater in very young 



children, and varies accord- 

 ing to different circumsta nces 

 (temperature, nutrition, 



FIG. 120. 



Graph of a muscular ^erk. 



Now, at the instant A of 

 the excitation, the muscle 

 does not respond ; at the 

 end of a time AB the " myo- 

 graphic curve" begins; it 

 therefore includes a " latent 

 period " AB of about TIR>U 

 of a second, according to 

 Tiegeistedt and Burdon- 



(*) Patrizi and Mensi (Giorn. R. Accad. Med. Torino, 1894, p. 61). 



