DIGESTIVE ENZYMES 165 



contents are hurried through the tube before absorption can take 

 place. 



Defecation is the act of expelling the feces. The bowel muscles 

 contract and the sphincter ani relaxes; the abdominal muscles 

 assist by compressing the organs from above. The dietary which 

 contains the largest proportion of waste material will leave the 

 greatest quantity of feces and lead to more frequent defecation 

 than one which is made up of digestible substances only. The 

 peristaltic action of the bowel is made more effective by the pres- 

 ence of a reasonable amount of matter to be acted upon. 



Clinical notes. Diarrhea is the passing of frequent loose or watery stools. 

 It occurs when the contents of the small intestine are hurried along too 

 rapidly by some irritating substance which causes excessive peristalsis and 

 a leakage of the watery portion of the blood. 



Constipation is caused by a too concentrated diet and slow peristalsis. 

 Since bile is a natural stimulant to the muscles of the bowel, constipation is 

 often associated with a torpid liver; it is also caused by lack of fluids in the 

 bowel. Therefore this is one reason why water is an important food. 



Origin of enzymes of the digestive fluids. They are formed, 

 usually, within the glandular cells of the organs which secrete 

 the fluids. Sometimes, by the fusion of a substance derived from 

 the cell with another called a pro-enzyme which it meets in the 

 fluid. 



For instance, the pancreas secretes two enzymes amylopsin and steapsin. 

 It also secretes trypsinogen, a pro-enzyme which unites with a special sub- 

 stance in the intestine to form the enzyme try p sin. In the one case (that 

 of amylopsin or of steapsin) the enzyme leaves the cells already formed, in 

 the other (that of trypsin) it is formed outside of the cells. 



As each digestive organ secretes its own fluid, so each fluid con- 

 tains its special enzymes for special purposes. For instance, the 

 enzymes or ferments of saliva cause rapid digestion of starches, 

 but not of eggs or meat. Those of the gastric juice assist the 

 digestion of eggs or meats, but not of starches. 



While it would probably be possible to digest the foods by the 

 use of chemical substances alone, as acids or alkalies, the process 

 would require such a high temperature that the body could not 

 endure it, and it would be so slow that we might starve while 

 waiting. The presence of enzymes not only accelerates the process 

 of digestion, but allows it to go on at the body temperature, hence 

 their great importance. 



