DIGESTION 195 



1. As perhaps first in consequence the stomach is a reservoir for food 

 and drink. Were there no such dilatation in the alimentary canal the 

 taking of ordinary food in meals would be impracticable, and man would 

 be in a somewhat literal sense the servant and not the master of his 

 digestive functions. Now that the stomach is occasionally removed 

 because of otherwise fatal disease, there is opportunity to observe 

 the value of the organ in this direction, for this function alone is unrepre- 

 sented elsewhere in the alimentary canal. Stomachs vary much in 

 size in different individals, and are liable to functional distention as 

 well as to almost tubular contraction, as already has been noted. A 

 fair estimate of the size of an average adult fundus in a filled condition 

 is perhaps a liter. By the ever-compressing force of this fundic reser- 

 voir the antrum is kept supplied with material on which to act, some- 

 what as the auricles of the heart are mainly reservoirs for the prompt 

 filling of the more active ventricles. 



2. The second in importance of the functions is perhaps the hydro- 

 lyzing of proteids and of albuminoids to forms which are absorbable 

 from the gut farther on. It seems probable that there is more difference 

 between peptic and tryptic proteolysis than is now generally recognized. 

 It is hard to define the relative importance of these two to the organ- 

 ism, yet the stomachless mammal probably thrives much better without 

 pepsin than he could without trypsin. 



3. Another function of the stomach, close or even equal to the last- 

 mentioned in importance, is the digestion of soluble carbohydrates begun 

 by the ptyalin in the mouth. The contents of the gastric fundus being 

 sometimes undisturbed for hours even, the major part of amylolysis takes 

 place sometimes at least in the stomach. Here the advancing neutrality 

 of reaction and perhaps soon a slight degree of acidity furnishes the 

 ptyalin its best medium for action on starches and on sugars. As we 

 have seen, the greater the proportion of carbohydrates in the stomach, 

 absorbing the free hydrochloric acid and so removing the pyloric 

 valve's closing-stimulus, the shorter the time the food remains in the 

 stomach. 



4. Another gastric function (Volhard) is probably the saponification of 

 emulsified fats. The importance of this activity is as yet unknown. 



5. A fifth function of the organ is to coagulate the caseinogen of milk 

 into casein and possibly to start it toward digestion by this change. The 

 enzyme rennin does this and besides, as has been said, may give the 

 stomach still other functions as yet unsuspected. 



6. A sixth action in digestion is the sterilization of food containing 

 bacteria, the free mineral-acid present in the gastric juice in amount of 

 1 per cent., more or less, being the chief agent in this direction. 



7. The long-continuance of the food in the relatively insensitive 

 stomach adapts the chyme in temperature for the best digestion and pre- 

 vents injury or at least functional interference with the duodenal glands 

 and muscles by chyme either too hot or too cold. This use depends 

 directly on the first function noted that the stomach is a reservoir. As 



