LARGE INTESTINE. 270 



tion closes the orifice in a really active manner : in the former 

 of these two cases defecation is produced. 



Defecation is a reflex phenomenon of expulsion, the centre 

 of which is found in the lower part of the cord, as is proved 

 by pathological cases. At the beginning of this reflex, a 

 vague sensation is experienced, which can hardly be defined, 

 a feeling of weight in the perineum produced by the presence 

 of the fbcal matter. The seat of this sensation, the desire, 

 is in the rectum only ; in the other parts of the large intes- 

 tine these substances are not normally felt. In cases of 

 artificial anus, however, following strangulated hernia, and 

 having their seat in any part of the intestinal tube, it has 

 been remarked that as the alvine matters approach the arti- 

 ficial orifice a vague sensation is felt, resembling that of the 

 necessary promptings of nature ; which seems to prove that 

 this sensation may be experienced in any part of the intes- 

 tinal tube, it being, perhaps, only due to the weight and 

 pressure of the faecal substances brought together in a mass 

 (Bert). 1 



Under the influence of this feeling a series of expulsive 

 efforts are made, which are reflex, as we have said, but are 

 under the influence of the will, either by increasing their 

 force or checking them. If the desire is not satisfied, an 

 anti-peristaltic movement takes place, beginning at the anal 

 sphincter, which drives the excrement back into the sigmoid 

 flexure, whence, after a time, they return to try the passage 

 again. If this attempt be resisted several times in succes- 

 sion, the rectum at length loses its sensibility, and the pres- 

 ence of the excrement ceases to give rise to the reflex action 

 which we are about to study ; this is the cause of the habitual 

 constipation of persons who neglect the signs mentioned, and 

 who soon find themselves obliged by artificial means (sup- 

 positories) to excite the dulled seosibility of the mucous 

 membrane of the rectum and of the nervous fibres which 

 govern the centripetal part of the reflex. 



If attention is paid to the promptings of this desire, a 

 reflex contraction of the muscular walls of the rectum takes 

 place naturally ; this is a genuine peristaltic movement, by 

 means of which the excrement is discharged into the anus, 

 the sphincter of which, dilating readily, offers no resistance. 

 If the faeces, indeed, are in an abnormally fluid state, the 



1 See Paul Bert, Art. Defecation, du " Nouveau Diet, de Mede- 

 cine et de Chirurgie Pratiques." Vol. X., p. 747. 



