118 THE FUNCTION 



" Their peristaltic motion is much fainter than that of the 

 small intestines. On the other hand, they experience to a greater 

 degree the pressure of the abdominal parietes, to which the 

 whole length of the colon is contiguous." 



On arriving in the large intestines, the mass of contents under- 

 goes fresh changes, at present unexplained, and is converted 

 into true excrement or faeces. z Here it is that a peculiar succus 

 entericus must be poured forth, for the secretion into the small is 

 probably nothing more than mucus and a simple watery fluid. 

 Tiedemann and Gmelin support, in some measure, the old idea of 

 the caecum being a subsidiary stomach, from its contents being 

 acid although acidity had disappeared higher up in the canal, 

 and more acid as the aliment is less digestible; and from albu- 

 men often reappearing suddenly in this part of the canal. Dr. 

 Prout found the fluids of the large intestines coagulate lymph 

 even as low as the rectum. 



The excrementitious mass, consisting of the indigestible part 

 of the food, the resinous colouring and fatty matters of the bile, 

 with intestinal mucus, loses its fluids gradually as it descends, 

 and in the lower part of the intestines becomes particularly dry.* 



The faeces appear to accumulate in the sigmoid flexure of the 

 colon, the lower and greater part of which, when empty, falls into 

 the pelvis, hanging doubled over. As the faeces accumulate, 

 this turns upon the rectum, until at length, like the stomach, its 

 greater arch is placed forwards and upwards, and its contents are 

 brought somewhat perpendicular to the upper end of the rectum. 

 When the accumulation amounts to a certain degree, that intestine 

 and the abdominal muscles and diaphragm are excited to simul- 

 taneous action, the whole contents pass down into and force open 

 the rectum, which, in its turn, is presently excited in the same 

 way, and the same powers b " overcome the resistance of the os 

 coccygis and of both sphincters, the inner of which is a re- 

 markable bundle of circular fibres, the outer, a truly cutaneous 

 muscle. After the excretion, the effort of the abdomen having 

 ceased, the levator ani chiefly retracts the intestine, which is 

 again closed by its sphincter." c 



z See Abernethy, Surgical Observations, Part II. p. 34. 



a The excrements of brutes have been analysed, but not to an extent capable 

 of affording general views. 



b Dr. O'Beirne, 1. c. 



c " All these parts may be seen as they exist in each sex, in Santorini's Posth. 

 Tables, xvi. and xvii." 



It is generally believed that the faeces collect in the rectum, till their quantity 



