426 MATER i A MEDIC A AND THERAPEUTICS. 



are as liquid at the ileo-ccecal valve as in the duodenum, i.e. 

 the effect of absorption as regards water is entirely neutralised. 

 The watery excretions, along with a small quantity of solids 

 and gases, are separated partly by osmosis from the vessels, 

 partly by the glands, the latter furnishing the succus entericus. 

 The activity of the glands is doubtless dependent upon many 

 influences connected with their vessels and nerves, and with 

 the quality of the blood, which are still imperfectly understood. 



The transit of the contents of bowels is effected by peri- 

 stalsis. The muscular coat is innervated by the vagus and 

 splanchnics, the former increasing peristalsis, the latter tending 

 to restrain or inhibit it, just as the vagus inhibits the heart. 

 Whilst the intestine is connected by these means with the cord 

 and brain, its movements are chiefly automatic and determined 

 by Auerbach's and Meissner's plexuses. The state of tension of 

 the wall, the internal pressure of faeces and gas, is the ordinary 

 stimulus of this mechanism ; but the nerves or muscles, or 

 both, are also stimulated by the bile ; and may be either excited 

 or depressed by many substances introduced through the blood, 

 as we shall see under the next head, as well as (inversely) by 

 the amount of blood supplied to them. In defecation the will 

 comes to the assistance of the automatic intestinal movements, 

 and effects evacuation of the bowels. 



General effects of evacuation of the bowels. The effects of 

 evacuation of the bowels are by no means purely local. On 

 the contrary, the whole system is influenced by this act, to no 

 great extent, it is true, under normal circumstances, but very 

 markedly when it amounts to actual purgation. When the 

 bowels are very freely moved, a certain amount of water is 

 directly or indirectly removed from the circulation. Bile is 

 swept out of the bowel, and the liver indirectly stimulated. 

 Certain solids and gases excreted by the intestinal wall, that is, 

 truly excrementitious substances, are thrown out of the system. 

 The circulation in the abdomen is disturbed: the vessels are 

 relieved from the pressure of the fasces ; the blood flows more 

 freely from the arteries through the portal system and li ver ; 

 whilst the volume of blood in the portal system and liver is 

 temporarily reduced by the watery excretion. The heart and 

 vessels generally are thus in turn relieved ; the blood pressure 

 in the systemic arteries falls ; the cerebral circulation is 

 especially depressed on account of its position, so that faintness 

 may be the result; the respiratory movements become easier; 

 the activity of the venous circulation is increased; and the 

 temperature falls. Amongst the abdominal vessels, the circu- 

 lation through the renal artery and vein is increased, and 

 with it the volume of urine secreted, diuresis being more 



