384 FUNCTIONS OF THE NERVOUS SYSTEM. 



selves, as from the spasmodic action of the larynx, excited by this ; and the 

 dislodgement of the morsel by an act of vomiting, is the most effectual means 

 of obtaining relief. Tenesmus and Strangury are well-known forms of spas- 

 modic muscular contraction, excited by local irritation acting through the 

 Spinal system. The abnormal action which leads to Abortion is frequently 

 excited in the same manner ; how far the uterus itself is called into contrac- 

 tion by the ordinary spinal nerves, is a question as yet undecided ; but the 

 facts already stated leave no doubt, that stimuli operating on these may act 

 upon it through the Sympathetic, into which their fibres pass ( 393). It will 

 be borne in mind, however, that, in abortion, as in ordinary parturition, many 

 muscles are called in, to aid the contractions of the uterus, which are strictly 

 under the dominion of the Spinal system. There is a form of Incontinence 

 of urine, which is very analogous to the morbid action just described ; the 

 sphincter has its due power ; but the stimulus to the evacuation of the bladder 

 is excessive in strength and degree, owing to the acridity of the urine or other 

 causes. The part of the bladder upon which this appears chiefly to act, is 

 the trigonum (which is well known to be more sensitive to the irritation of 

 calculi, than the rest of the internal surface) ; and Sir C. Bell advises young 

 persons who suffer during the night from this very disagreeable complaint, to 

 lie upon the belly instead of the back, ,so that the contact of the urine with 

 the trigonum may be delayed as long as possible. 



505. One of the most familiar examples of the pathological excitement of 

 the true Spinal system is the act of Vomiting; and, as Dr. M. Hall justly 

 remarks, the special function of this system nowhere receives better illustra- 

 tion. The act may be excited in various ways. Thus, it results from the 

 tickling of the fauces with a feather or with the finger ; but if the feather be 

 carried too far down, an act of deglutition is induced instead of vomiting.* 

 In this instance the glosso-pharyngeal, and perhaps also the fifth pair, are the 

 nerves by which the stimulus is conveyed to the Medulla Oblongata. Vomit- 

 ing, again, may be induced by substances introduced into the stomach ; and 

 here the pneumogastric is evidently the excitor. When it takes place as a 

 result of pregnancy, or of some intestinal irritation, the stimulus must be con- 

 veyed, either through one of the ordinary Spinal nerves, or through the Sym- 

 pathetic. But it may also be occasioned by the sight, smell, or taste of any 

 disagreeable object, or by the mere conception of it, or by mental emotion 

 simply. In this case, the stimulus appears to be received by the ganglia of 

 special sense, and to be transmitted by them to the muscles concerned, as by 

 the Spinal Cord or Medulla Oblongata in the former case. When Vomiting 

 is excited by the introduction of emetic substances into the blood, it is proba- 

 ble that their stimulation chiefly operates through the extended plexus of 

 nerves, spread out by the Sympathetic upon the walls of the blood-vessels ; 

 but the irritant action of the substance upon the nervous centres may be also 

 concerned. In regard to the mechanism by which the act of Vomiting is 

 produced, considerable difference of opinion has existed. The old doctrine 

 was, that it was solely occasioned by the contraction of the stomach itself; 

 but Magendie proved that this could not be the case, by substituting a bladder 

 for the stomach of an animal, and then injecting a solution of tartarized anti- 

 mony into its blood, which immediately caused the emptying of the bladder, 

 by the pressure of the surrounding muscles ; these muscles he considered to 



* This has been the cause of many accidents. Patients have tickled the fauces with a 

 feather in order to excite vomiting; and, having introduced it too far into the pharynx, it has 

 been Brawn out of their fingers by the muscles of deglutition, and carried into the oasophagus. 

 Similar accidents have occurred with the rectum-bougie, and female catheter, as well as with 

 probes, &c., introduced into the male urethra; all the orifices being furnished with a kind of 

 ingestive power, which isclearly the result of Reflex action. 



