518 SYSTEM OF THE GREAT SYMPATHETIC. 



nerves belonging to the sympathetic system. If the facial or hypo- 

 glossal, or the anterior root of a spinal nerve be irritated, the con- 

 vulsive movement which follows is instantaneous, violent, and only 

 momentary in its duration. But if the semilunar ganglion or its 

 nerves be subjected to a similar experiment, no immediate effect is 

 produced. It is only after a few seconds that a slow, vermicular, 

 progressive contraction takes place in the corresponding part of the 

 intestine, which continues for some time after the exciting cause 

 has been removed. 



Morbid changes taking place in organs supplied by the sympa- 

 thetic present a similar peculiarity in the mode of their produc- 

 tion. If the body be exposed to cold and dampness, for example, 

 congestion of the kidneys shows itself perhaps on the following 

 day. Inflammation of any of the internal organs is very rarely 

 established within twelve or twenty -four hours after the application 

 of the exciting cause. The internal processes of nutrition, together 

 with their derangements, which are regarded as especially under 

 the control of the great sympathetic, always require a longer time 

 to be influenced by incidental causes, than those which are regulated 

 by the nerves and ganglia of the cerebro-spinal system. 



In the head, the sympathetic has a close and important connec- 

 tion with the exercise of the special senses. This is illustrated 

 more particularly in the case of the eye, by its influence over the 

 alternate expansion and contraction of the pupil. The ophthalmic 

 ganglion sends off a number of ciliary nerves, which are distributed 

 to the iris. It is connected, as we have seen, with the remaining 

 sympathetic ganglia in the head, and receives, beside, a sensitive 

 root from the ophthalmic branch of the fifth pair, and a motor root 

 from the oculo-motorius. The reflex action by which the pupil 

 contracts under a strong light falling upon the retina, and expands 

 under a diminution of light, takes place, accordingly, through this 

 ganglion. The impression conveyed by the optic nerve to the 

 tubercula quadrigemina, and reflected outward by the fibres of 

 the oculo-motorius, is not transmitted directly by the last named 

 nerve to the iris ; but passes first to the ophthalmic ganglion, and 

 is thence conveyed to its destination by the ciliary nerves. 



The reflex movements of the iris exhibit consequently a some- 

 what sluggish character, which indicates the intervention of a part 

 of the sympathetic system. The changes in the size of the pupil 

 do not take place instantaneously, with the variation in the amount 

 of light, but always require an appreciable interval of time. If 



