450 THE NERVOUS SYSTEM. 



sions of pain, and have excited movements in the muscular 

 organs supplied from the irritated part. 



In the case of pain excited, or movements affected by the 

 mind, it may be supposed that the conduction of impressions 

 is effected through the cerebro-spinal fibres which are mingled 

 in all, or nearly all, parts of the sympathetic nerves. There 

 are no means of deciding this ; but if it be admitted that the 

 conduction is effected through the cerebro-spinal nerve-fibres, 

 then, whether or not they pass uninterruptedly between the 

 brain or spinal cord and the part affected, it must be assumed 

 that their mode of conduction is modified by the ganglia. For, 

 if such cerebro-spinal fibres are conducted in the ordinary 

 manner, the parts should be always sensible and liable to the 

 influence of the will, and impressions should be conveyed to 

 and fro instantaneously. But this is not the case ; on the con- 

 trary, through the branches of the sympathetic nerve and its 

 ganglia, none but intense impressions, or impressions exagger- 

 ated by the morbid excitability of the nerves or ganglia, can 

 be conveyed. 



Respecting the general action of the ganglia of the sympa- 

 thetic nerve, little need be said here, since they may be taken 

 as examples by which to illustrate the common modes of action 

 of all nerve-centres (see p. 382). Indeed, complex as the sym- 

 pathetic system, taken as a whole, is, it presents in each of its 

 parts a simplicity not to be found in the cerebro-spinal system : 

 for each ganglion with afferent and efferent nerves forms a 

 simple nervous system, and might serve for the illustration of 

 all the nervous actions with which the mind is unconnected. 

 But it will be more convenient to consider the ganglia now in 

 connection with the functions that they may be supposed to 

 control, in the several organs supplied by the sympathetic sys- 

 tem alone, or in conjunction with the cerebro-spinal. 



The general processes which the sympathetic appears to in- 

 fluence, are those of involuntary motion, secretion, and nutri- 

 tion. 



Many movements take place involuntarily in parts supplied 

 with cerebro-spinal nerves, as the respiratory and other spinal 

 reflex motions ; but the parts principally supplied with sym- 

 pathetic nerves are usually capable of none but involuntary 

 movements, and when the mind acts on them at all, it is only 

 through the strong excitement or depressing influence of some 

 passion, or through some voluntary movement with which the 

 actions of the involuntary part are commonly associated. The 

 heart, stomach, and intestines are examples of these state- 

 ments ; for the heart and stomach, though supplied in large 



