276 DIGESTION. 



To sum up the whole process of the digestion of starch, it may be stated, in general 

 terms, that this principle, when hydrated, which is the usual condition in which it is 

 taken into the stomach of the human subject, is slightly acted upon by the saliva, both 

 in the mouth and after it has passed into the stomach ; when it is taken raw, it is hy- 

 drated in the stomach and usually undergoes no transformation into sugar until it has 

 passed into the small intestine ; and, when it passes out at the pylorus, mainly by the ac- 

 tion of the pancreatic juice but with the assistance of the intestinal juice, it is transformed 

 into glucose and in this form is absorbed. 



We have already followed out the digestion of sugar as far as the small intestine. 

 Glucose undergoes no change in the stomach and is taken directly into the circulation. 

 It is probable, also, that a small quantity of cane-sugar may in like manner be taken up 

 by the blood-vessels of the intestinal mucous membrane. It has been shown that a small 

 quantity of cane-sugar is transformed into glucose in the stomach, but, as we noted in 

 treating of stomach-digestion, the quantity is inconsiderable, and the transformation de- 

 pends simply upon the presence of a free acid in the gastric juice. 



As most of the saccharine principles of food exist in the form of cane-sugar, it is the 

 action of the digestive fluids upon this variety of sugar which possesses the greatest phys- 

 iological interest. As cane-sugar passes from the stomach into the duodenum it is al- 

 most instantly transformed into glucose. This fact has lately received additional con- 

 firmation in the case of intestinal fistula observed by Bnsch. In this case, when cane- 

 sugar was introduced in quantity into the stomach, fasting, the fluid which escaped from 

 the upper end of the intestine contained a small quantity of glucose but never any cane- 

 sugar. 



It now becomes a question whether the transformation of cane-sugar into glucose be 

 effected by the bile, the intestinal juice, or the pancreatic juice. The pancreatic juice 

 and the intestinal juice are the two fluids which might be supposed to have this effect ; 

 for it has been repeatedly demonstrated that the bile has of itself no direct action upon 

 any of the alimentary principles. This point is settled by the experiments of Busch upon 

 the lower end of the intestine, in his case of fistula. Matters introduced into this lower 

 opening came in contact with the intestinal juice only. He found that cane-sugar, ex- 

 posed thus to the action of the intestinal juice, was not converted into glucose, but a 

 large portion of it was found in the faeces. His observations also indicate that cane- 

 sugar is not readily absorbed by the intestinal mucous membrane until it has been trans- 

 formed into glucose. 



Out of the body, the pancreatic juice is capable, if kept but for a short time in con- 

 tact with any of the saccharine principles, of transforming them into lactic acid. The 

 contents of the small intestine are sometimes alkaline or neutral and are sometimes acid. 

 When a very large quantity of sugar has been taken, a part of it may be converted in the 

 intestine into lactic acid, and this may happen with the sugar which results from the 

 digestion of starch ; but, under ordinary conditions, starch and cane-sugar are readily 

 changed into glucose and are absorbed without undergoing farther transformation. All 

 the varieties of sugar, after they have been absorbed by the portal vein and carried to 

 the liver, are here transformed into glucose, the only form, apparently, under which they 

 can be used in nutrition. 



Action of the Pancreatic Juice upon Nitrogenized Principles. We have frequently had 

 occasion to insist upon the great relative importance of intestinal digestion, and it has 

 been apparent that, in the stomach, the process of disintegration of food is not final, 

 even as regards many of the nitrogenized principles, but is rather preparatory to the 

 complete liquefaction of these principles, which takes place in the small intestine. The 

 experiments, already referred to, of Bernard, in which the pancreas has been partially 

 destroyed in dogs, show rapid emaciation, with great voracity, and the passage, not only 

 of unchanged fats and starch, but of undigested nitrogenized matter in the dejections. 



