66 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



Function of the Spinal or Reflex System. — As 



already said, the function of this system is to preside 

 over and control all the routine work of the body — 

 work so constantly necessary that it can not be left to 

 the conscio-voluntary system, which is occupied with 

 other and higher work. Thus the beating of the heart, 

 the play of the respiratory muscles, the movements of 

 the stomach and intestines, are under the control of this 

 system, which never sleeps night or day. The conscio- 

 voluntary system alone sleeps. The passage of control 

 from one system to the other is well seen in the act of 

 swallowing. The food is chewed, then gathered by the 

 tongue, then pressed back into the throat ; so much is 

 under control of the voluntary system. As soon as it 

 touches the throat it is seized by the involuntary sys- 

 tem and hurried on to the stomach. Nevertheless, there 

 are all gradations between reflex and conscio-voluntary 

 movements. The movements of stomach, intestines, and 

 heart are not only involuntary, but also, in health, un- 

 conscious; the acts of swallowing, sneezing, coughing, 

 are involuntary, but not unconscious ; the act of breath- 

 ing is not only conscious, but also partly controlled by 

 volition. 



When the conscio-voluntary system is in full activity 

 it takes possession of the consciously sensitive surfaces 

 and the voluntary muscles, so that the reflex system is in 

 abeyance except under conditions of extreme stimula- 

 tion or pain, in which case the reflex takes hold because 

 the conscio-voluntary is too slow. But when the conscio- 

 voluntary control is withdrawn, as in sleep, or paralyzed, 

 as in section of the cord or of a nerve, then the reflex is 

 far more active, as shown by the unconscious, involun- 

 tary movements of hand or foot on the least irritation. 



Illustration by Telegraphy. — The system of telegraphy 

 already used to illustrate the action of the conscio-vol- 



