RECAPITULATION AND PATHOLOGICAL APPLICATIONS. 223 



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 suf- 

 fer 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. 



301. 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 5f 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 exciter. 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 blodti ( 199), it is 

 probable 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 occasioned by the simple 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 

 be the diaphragm and abdominal muscles, the conjoint actions of which would 

 be a peculiarity observed in no other instance. By Dr. M. Hall, on the other 

 hand, it is maintained that the act of vomiting is, like the expulsion of the 

 foetus, urine, fa3Ces, &c., an expiratory effort, modified in its effects by the 

 peculiar condition of the sphincters. It bears, indeed, great resemblance to 

 the act of coughing ; differing chiefly in this, that in Vomiting the larynx is 

 closed during the whole operation, whilst it is only closed momentarily in 

 coughing ; and also that in coughing the cardiac 'orifice of the stomach is 

 closed, whilst in vomiting it is opened. In this view, the accuracy of which 



* 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 pha- 

 rynx, it has been drawn 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 is clearly the result of 

 Reflex action. 



