THE NERVOUS SYSTEM. 155 



the parts supplied with nerves from the sympathetic are shown to be, in 

 a measure, independent of the brain and spinal cord; this independent 

 maintenance of their action being, without doubt, due to the fact that 

 they contain, in their own substance, the apparatus of ganglia and nerve- 

 fibres by which their motions are immediately governed. 



It seems to be a general rule, at least in animals that have both cere- 

 bro-spinal and sympathetic nerves much developed, that the involuntary 

 movements excited by stimuli conveyed through ganglia are orderly and 

 like natural movements, while those excited through nerves without 

 ganglia are convulsive and disorderly; and the probability is that, in the 

 natural state, it is through the same ganglia that natural stimuli, impress- 

 ing centripetal nerves, are reflected through centrifugal nerves to the 

 involuntary muscles. As the muscles of respiration are maintained in 

 uniform rhythmic action chiefly by the reflecting and combining power 

 of the medulla oblongata, so are those of the heart, stomach, and intes- 

 tines, by their several ganglia. And as with the ganglia of the sympa- 

 thetic and their nerves, so with the medulla oblongata and its nerves dis- 

 tributed to the respiratory muscles, if these nerves of the medulla 

 oblongata itself be directly stimulated, the movements that follow are con- 

 vulsive and disorderly; but if the medulla be stimulated through a cen- 

 tripetal nerve, as when cold is applied to the skin, then the impressions 

 are reflected so as to produce movements which, though they may be very 

 quick and almost convulsive, are yet combined in the plan of the proper 

 respiratory acts. 



Among the ganglia of the sympathetic nerves to which this co-ordina- 

 tion of movements is to be ascribed, must be reckoned, not those alone 

 which are on the principal trunks and branches of the sympathetic ex- 

 ternal to any organ, but those also which lie in the very substance of the 

 organs; such as those of the heart (p. 125, Vol. I.). Those also may be 

 included which have been found in the mesentery close by the intestines, 

 as well as in the muscular and sub-mucous tissue of the stomach and in- 

 testinal canal (pp. 244, 255, Vol. I.)., and in other parts. The extension 

 of discoveries of such ganglia will probably diminish yet further the num- 

 ber of instances in which the involuntary movements appear to be effected 

 independently of nervous influence. 



Respecting the influence of the sympathetic system on various physi- 

 ological processes, see Heart (p. 127, Vol. I.), Arteries (p. 152, Vol. I.), 

 Animal Heat (p. 316, Vol. I.), Salivary Glands (p. 233, Vol. I.), Stomach 

 (p. 252, Vol. I.), Intestines (p. 255, Vol. I.). These are parts which have 

 been specially investigated. But they are not in any way exceptional. 

 All physiological processes must, of necessity, either directly or through 

 vaso-motor fibres, be under the influence of the Sympathetic system. 



Influence of the Nervous System on Nutrition. It has been 

 held that the nervous svstem cannot be essential to a healthy course of 



