390 CHANGES IN THE SMALL INTESTINE. [BOOK n. 



ach changes leading to emulsion, similar to those which, as we 

 shall see, are carried out in the small intestine. 



But such cases as these cannot be regarded as typical cases of 

 gastric digestion, and in man, at all events, living on a mixed 

 diet the work of the stomach appears to be to a large extent 

 preparatory only to the subsequent labours of the intestine. 

 It is true that our information on this matter is imperfect, 

 being chiefly drawn from the study of cases of gastric or duo- 

 denal fistula, in which probably the order of things is not 

 normal, or being in large measure deductions from experiments 

 on animals, whose economy in this respect must be largely dif- 

 ferent from our own ; but we are probably safe in concluding 

 that, in ourselves, the chief effect of gastric digestion is by 

 means of the disintegration spoken of above to reduce the 

 lumps of food to the more uniform chyme and so to facilitate 

 the changes which take place in the small intestine. During 

 that disintegration some of the proteid in the meal is con- 

 verted into peptone ; and the peptone so formed is probably 

 absorbed at once ; but much proteid remains unchanged or at 

 least is not converted into peptone, and the fats and starches 

 undergo in themselves very little change indeed. 



In the act of swallowing, no inconsiderable quantity of air is 

 carried down into the stomach, entangled in the saliva, or in the 

 food. This is returned in eructations. When the gas of eruc- 

 tation or that obtained directly from the stomach is examined, 

 it is found to consist chiefly of nitrogen and. carbonic acid, the 

 oxygen of the atmospheric air having been largely absorbed. 

 In most cases the carbonic acid is derived by simple diffusion 

 from the blood, or from the tissues of the stomach, which sim- 

 ilarly take up the oxygen. In many cases of flatulency, however, 

 it may arise from a fermentative decomposition of the sugar 

 which has been taken as such in food or which has been produced 

 from the starch, the gas being either formed in the stomach or 

 passing upwards from the intestine through the pylorus. 



The enormous quantity of gas which is discharged through 

 the mouth in cases of hysterical flatulency, even on a perfectly 

 empty stomach, and which seems to consist largely of carbonic 

 acid, "presents difficulties in the way of explanation ; it is pos- 

 sible that it may be simply diffused from the blood, but it is 

 also possible that in many cases it is derived from air which 

 the patient has hysterically swallowed, the oxygen having been 

 removed, in the stomach, by absorption and replaced by carbonic 

 acid. 



In the Small Intestine. 



230. The semi-digested acid food, or chyme, as it passes 

 over the biliary orifice, causes as we have seen ( 215) gushes 

 of bile, and at the same time the pancreatic juice flows into the 



