THE SMALL INTESTINE 97 



one, favoring one type of organism and restraining another. 

 Even though it had no such influence, the intestinal 

 bacteria might be expected to multiply in its absence, for 

 the simple fact of delayed absorption would suffice to bring 

 this about. Our best defense against excessive fermenta- 

 tion and putrefaction is in the early and complete removal 

 of the food from the sphere of action of micro-organisms. 



Summary. The secretions flowing into the small intes- 

 tine supply enzymes in sufficient number and variety to 

 accomplish the digestion of all common foods. The trans- 

 formation of starch to maltose begun in the stomach is 

 completed by the pancreatic amylase. The resolution of 

 proteins into the simple structural units from which their 

 molecules are built is carried out under the influence of 

 trypsin and perhaps of erepsin. The last-named enzyme 

 is supposed by many to work upon the tryptic products as 

 they pass through the lining cells on their way to the blood. 

 Fats are hydrolyzed by the pancreatic lipase, with the 

 formation of glycerin and fatty acids, the latter being 

 in some measure converted to soaps. . The disaccharids are 

 changed to monosaccharids, a work attributed to the in- 

 testinal juice. Fermentation caused by bacteria has been 

 taking place along with the strictly normal processes. 

 The most evident products are organic acids, which may or 

 may not be fully neutralized by the alkaline secretions. 



Protection Against Self-digestion. There has been 

 much discussion of the fact that the proteolytic enzymes 

 in the digestive tract do not ordinarily attack its mucous 

 membrane. They may do so after death and when the 

 tissues are in an abnormal condition, as in case of gastric 

 ulcer, the juices may strongly antagonize the healing pro- 

 cess. It is often asserted that there is a definite chemical 

 difference between the proteins of living and of lifeless 

 matter. A recent explanation of the resistance which 

 living cells offer to digestion is based on the apparent fact 

 that such cells form bodies which have the capacity to neu- 

 tralize enzymes in fixed proportions. The name of anti- 

 enzymes has been applied to such protective substances. 

 7 



