300 ANATOMY FOR NURSES [Chap. XV 



intestine, and since it contains the digestive enzjines received 

 in the duodenum, the process of digestion and absorption 

 continues. 



By the abstraction of all the soluble constituents, and especially 

 by the withdrawal of water, the liquid contents become, as they 

 approach the rectum, changed into a firm and solid mass of waste 

 matters, ready for ejection from the body, and calK-d feces. 



Action of bacteria in large intestine. — Protein putrefaction 

 due to the action of bacteria is a constant and normal occurrence 

 in the large intestine. A long list of end products result from 

 this putrefaction. Some are given off in the feces, others are ab- 

 sorbed and later excreted in the urine. The action of bacteria is 

 considered of doubtful value. It is possible that they may act 

 upon the cellulose of vegetable foods and render it useful in nu- 

 trition. A conservative view is that bacteria confer no positive 

 benefit, but under normal conditions the body is able to neutralize 

 their action. 



The feces. — The feces consist of: (1) the undigested and 

 indigestible parts of the food, (2) the products of bacterial de- 

 composition, (3) great quantities of bacteria of difi'erent kinds, 

 (4) bile and other secretions, (5) enzymes, and (6) inorganic salts. 

 The color of feces is due to the presence of pigments derived from 

 the bile. 



Defecation. — The anal canal is guarded by an internal sphincter 

 muscle of the involuntary type, and an external sphincter that is 

 voluntary, but both are supplied with nerves from the central 

 nervous system and consequently defecation is a voluntary act. 

 Normally the rectum is empty until just before defecation. Various 

 stimuli (depending on one's habits) will produce peristaltic action of 

 the colon, so that a small quantity of feces enters the rectum. 

 This irritates the sensory nerve endings and causes a desire to 

 defecate. The voluntary contraction of the abdominal muscles, 

 the descent of the diaphragm, and powerful peristalsis of the colon 

 all combine to empty the colon and rectum. 



One of the commonest causes of constipation is the retention 

 of feces in the rectum because of failure to act on the desire for 

 defecation. After feces once enter the rectum there is no retro- 

 peristalsis to carry it back to the colon, and the sense of irritation 

 becomes blunted. The desire may not recur for twenty-four hours, 



