470 INFLUENCE OF THE NERVOUS SYSTEM 



to the muscles of the larynx than to those of the mouth. Every one must 

 have noticed how much the impediment of Stammerers is increased, when 

 they are particularly anxious to speak fluently. 



CHAPTER IX. 



INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS. 



620. OF the modes in which the Nervous System influences the Organic 

 Functions, a part have been already considered. It has been shown ( 183) 

 that it is concerned in providing the conditions, either immediate or remote, 

 under which alone these functions can be performed ; so that, when its ac- 

 tivity ceases, they cannot be much longer maintained. The first mode in 

 which it operates upon them is, therefore, by producing sensible movements 

 in the Muscles or other contractile organs, which can be stimulated to action 

 through it ; and the contractions thus induced have usually an important effect 

 upon them, which varies, however, in each individual case. Thus, the pro- 

 cess of Nutritive Absorption, which is the very first stage in the operations of 

 Vegetative Life, and which is accomplished in Plants by the accidental con- 

 tact of the alimentary materials with the radical fibres, cannot take place in 

 Animals, until the muscular apparatus of prehension has been set in action by 

 the Will, that of deglutition by the Reflex Function, and that of the intestinal 

 canal by direct stimulation, the two former kinds of contraction being ac- 

 complished entirely through the Nervous System, and the latter being influ- 

 enced by it. The Circulation of Blood, too, is chiefly effected, in the higher 

 Animals at least, by the contractions of a muscular organ of impulsion ; which 

 contractions, though not essentially dependent upon Nervous action, are 

 nevertheless greatly influenced by it. The function of Respiration, again, 

 cannot be maintained even for a short time, without muscular movement, ex- 

 cited through the Nervous System. The functions of Nutrition and Secre- 

 tion are more independent of it ; taking place, as in Plants, so long as the 

 conditions are supplied by other functions, without any sensible movements 

 being actually concerned in them. We shall presently see, however, that 

 they are subject to a peculiar kind of Nervous influence, which does not 

 manifest itself in obvious movement, but in altered performance of the inti- 

 mate processes themselves ; showing itself in the character of the organized 

 tissue, or of the secreted product. The act of Excretion is, like ingestion, 

 entirely performed by Muscular movement, dependent upon Nervous agency. 

 Now, wherever such movements of distant organs are usually performed in 

 connection with each other, there is an obvious channel for one kind of sym- 

 pathy between them ; an interesting example of this, is the contraction of the 

 Uterus, which may be frequently made to occur, when that organ is in a re- 

 laxed state at the conclusion of labour, by applying suction or other irritation 

 to the nipple. 



G21. Sympathetic movements of this kind may be excited either through 

 the Cerebro-Spinal, or the Gangliouic systems; and we shall be guided in 

 our determination of their channel in each particular case, by the distribution 

 of these systems respectively to the organ aflectcd. The sympathetic move- 

 ments of the Muscles of Animal life appear to be chiefly, if not entirely, ex- 



