414 PROPERTIES AND FUNCTIONS 



other upon the middle of. the arm between the shoulder 

 and elbow, we shall feel a muscle contract and form a 

 hard cord. This muscle is attached to the shoulder bone 

 at one end, and at the other, to one of the bones of the 

 fore arm, and thus when it contracts or shortens, the ne- 

 cessary effect is to bend the arm at the elbow and bring 

 the hand to the head. 



In man and the highest order of animals there are two 

 classes of muscles, those which contract under the influ- 

 ence of the will and those which contract independent of 

 it. The former are called voluntary and the latter in- 

 voluntary. The heart regularly contracts from the first 

 moments of our existence to the last, as well when we 

 are asleep as awake. It is not in the least influenced by 

 the will. The regular contractions of the stomach also 

 are entirely and absolutely independent of volition. The 

 process of respiration is usually performed by means of 

 the involuntary muscles. We can for a few momenta 

 cease to respire if we will, and if the involuntary muscles 

 or the nerves leading to them are involved in any disease 

 which unfits them for the performance of their duty, respi- 

 ration may be performed under the control of the will, 

 but this is extremely laborious and cannot be continued 

 for any great length of time. Thence it would seem that 

 the organs of respiration were furnished with voluntary 

 and involuntary muscles, and this fact has been proved 

 by the most satisfactory experiments. 



Locomotion is performed altogether by means of the 

 voluntary muscles. We will to move and immediately 

 these muscles are in action. 



If the contraction of the heart and the muscles of re- 

 spiration were under the entire control of the will, the 

 constant and unremitted exertions of the mind would be 

 required there would be no time for rest or sleep; for if 

 there was a suspension of consciousness there would of 

 course be a suspension of circulation and respiration, and 

 immediate death would be the consequence. 



Animals are alone endowed with a proper muscular 

 apparatus, but some plants have the power of motion in 

 an eminent degree. Their fibres therefore must have the 

 power of contraction, and they must be endowed with 



