154 HAND-BOOK OF PHYSIOLOGY. 



sufficiently numerous, irritations of the semilunar ganglia, the splanchnic 

 nerves, the thoracic, hepatic, and other ganglia and nerves, have elicited 

 expressions of pain, and have excited movements in the muscular organs 

 supplied from the irritated part. 



In the case of pain, or of movements affected by mental conditions, 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 contrary, through the branches of the sympathetic nerve and its 

 ganglia, none but intense impressions, or impressions exaggerated by the 

 morbid excitability of the nerves or ganglia, can be conveyed. 



Respecting the general action of the ganglia of the sympathetic nerve, 

 in reflex or other Actions, 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. 83, Vol. II.). Indeed, complex as the sympathetic 

 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. 



The parts principally supplied with sympathetic 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 influ- 

 ence 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 statements; for the heart 

 and stomach, though supplied in large measure from the pneumogastric 

 nerves, yet probably derive through them few filaments except such as 

 have arisen from their ganglia, and are therefore of the nature of sym- 

 pathetic fibres. 



The parts which are supplied with motor power by the sympathetic nerve 

 continue to move, though more feebly than before, when they are sepa- 

 rated from their natural connections with the rest of the sympathetic sys- 

 tem, and wholly removed from the body. Thus, the heart, after it is taken 

 from the body, continues- to beat in Mammalia for one or two minutes, 

 in reptiles and Amphibia for hours; and the peristaltic motions of the 

 intestine continue under the same circumstances. Hence the motions of 



