FECES 65 



3. Inverting enzymes, which convert disaccharides into mono- 

 saccharides. They are three in number maltase, invertase, 

 and lactase. 



4. Nuclease, an enzyme which acts upon nucleic acids. 



5. Secretin, formed in the intestinal mucosa as prosecretin 

 and changed to secretin by hydrochloric acid. It is not an 

 enzyme but comes under the class of bodies known as hormones. 



Digestion in the Large Intestine. Here the secretion is 

 composed mainly of mucus, is scanty, alkaline in reaction, 

 and has no enzymes of its own. Digestive changes occur, 

 however, for some time, and are due to enzymes brought 

 down from above. Extensive bacterial decomposition takes 

 place. 



Bacteria may be found in any portion of the intestinal tract, 

 and their activity is always involved in ordinary digestion. 

 But it is not essential to health in mammals. Guinea-pigs 

 removed from the mother by Cesarean section, reared aseptic- 

 ally, and fed on sterile milk grew as fast as those reared in 

 the ordinary way. The alimentary canal remained free from 

 bacteria. Chickens, on the other hand, reared under similar 

 conditions lived only eighteen days. It is possible that the 

 vegetable food requires the aid of bacteria to insure its proper 

 digestion. 



As the result of the action of bacteria on proteins there are 

 formed indol, phenol, and skatol. These are excreted in the 

 feces and partly reabsorbed, conjugated with sulphuric acid, 

 and excreted in the urine. Indol, in this way, appears in 

 the urine as indican. In some animals a cellulose-destroying 

 enzyme leads to the formation of sugar, but in man, although 

 cellulose is to some extent destroyed, no sugar is formed. The 

 contents of the large intestine are usually acid, but the wall 

 itself is alkaline in reaction. 



Feces. The feces vary in composition and amount with 

 the nature and the quantity of the food. On a mixed diet the 

 amount in twenty-four hours varies from 100 to 500 grams 

 in weight. Its constituents are indigestible materials, un- 

 digested foodstuffs, intestinal secretions, products of bacterial 

 action, cholesterin, excretin, mucus, pigment, salts, gases, 

 and microorganisms. Among the products of bacterial action 

 are indol (C 8 H 7 N) and skatol (C 9 H 9 N), which are crystallizable 

 5 



