NERVOUS ACTION. 387 



when aliment lias been introduced into the mouth, is 

 necessary to assist in mastication, deglutition, &c. ; and 

 when a powerful light falls upon the eye, the closing of the 

 pupil is no less needful to intercept the luminous rays, and 

 to prevent them striking on the bottom of the eye, dazzling 

 the sight, and otherwise injuriously affecting the organ. 

 The acts above cited are known as physical nervous actions, 

 since they take their origin in a physical impression on 

 some part of the economy. By means of this mechanism 

 are sustained all the important vital functions, such as 

 circulation, respiration, digestion, &c. In all such cases, 

 the stimulus must be properly regulated as regards charac- 

 ter, force, time, and direction, as otherwise it might prove 

 not only abortive but even eminently injurious. 



In physical nervous actions, the primary impression and 

 the resulting movement may, one or both, be taken cogni- 

 sance of by the mind, or vice versa. Thus, when a limb is sud- 

 denly withdrawn as a result of contact of the toes with a hot 

 or other irritating body, both impression and result are quite 

 patent to the mind, though the muscles of the leg were in 

 action before the will had time to command. The act of 

 breathing, of which we are quite conscious, results from an 

 impression made by the circulating blood on the system, 

 but especially on the lungs and brain, and of which we are 

 unconscious, unless we for a time voluntarily suspend the 

 respiratory process. Lastly, as an example of the exercise 

 of both without the mind perceiving it, may be mentioned 

 the movement of the intestines, as a result of contact between 

 the ingesta and the mucous membrane. It may be con- 

 cluded, that though the mind may take cognisance of, and 

 even perfect such an action commenced independently of 

 it, still in no case is perception or the exercise of the will 

 necessary to the performance of such an act. 



