98 PHYSIOLOGY. 



made up mostly of gelatine, as the membranes, cartilages, 

 skin, vessels, &c., have but a slight degree of contractility ; 

 that they possess it, in some measure, is evident from the 

 contraction of blood-vessels by the application of stimulants. 



17. There are two modifications of contractility); one of 

 which depends for its exercise on the brain, and the other 

 does not. For example, if we wish to bend the arm, we have 

 but to transmit to the muscles of the arm, through the nerves 

 with which it is supplied from the brain, a volition, or act 

 of the will, to that effect, and the arm bends. Here we per- 

 ceive that the influence of the brain is necessary to contrac- 

 tility or motion. 



18. {When certain muscles are deprived of this power of 

 contracting, they are said to be paralyzed, or the limb is 

 called paralytic.} (When they have it in excess, they are in 

 a state of spasm, or convulsion^ We see such a state often 

 brought on by excessive drinking. There is no cure for this 

 but by entirely breaking off the habit. 



19. The other kind of contractility belongs to every part 

 of the body. It does not depend for its existence on the 

 brain, nor is it at all under the influence of the will, or 

 accompanied with consciousness. Thus the heart and the 

 stomach contract constantly under the application of their 

 proper stimuli, but the brain is not conscious of it ; their 

 action is entirely beyond its jurisdiction. This form of con- 

 tractility has been called insensible. 



20. It is owing to the insensible, organic contractility, 

 that the blood circulates in the capulary vessels ; the lymph 

 and the chyle in the absorbents and lacteals, and all the 

 secreted fluids through the vessels that prepare them. In 

 all animals destitute of a heart, the fluids can only be moved 

 by this insensible contractile power. A similar force is 

 supposed to exist in the vessels of plants. 



21. These two kinds of contractility, viz., the sensible 

 and insensible, have been compared to the hour and minute 

 hands on the dial of a clock, which are both moved by the 



