DIGEST I OX 391 



peptone stage while still in the stomach, leaving for the juices 

 that act on it in the intestine only its further hydrolysis to 

 amino-acids, etc. But we may safely assume that, in the case of 

 a man living on an ordinary mixed diet, a good deal of the food 

 proteins passes through the pylorus chemically unchanged, or 

 having undergone only the first steps of hydration. For, even a 

 few minutes after food has been swallowed, especially liquid food 

 or water, the pyloric sphincter may relax and allow the stomach 

 to propel a portion of its contents into the intestine ; and such 

 relaxations occur at intervals as digestion goes on, although it is 

 not for several hours (three to five) that the greater portion of 

 the food reaches the duodenum. During this period the acidity 

 has at first been constantly increasing, although for a time the 

 hydrochloric acid has combined, as it is formed, with the proteins 

 of the food. Then comes a stage where the hydrochloric acid 

 has so much increased that, after combining with all the proteins, 

 some of it remains over as free acid. After a time the total acidity 

 begins to fall, the partially digested proteins continually passing 

 on through the pylorus, while a considerable proportion is so 

 fully digested as to be absorbed by the gastric mucous membrane 

 itself. Thus, in one experiment on the digestion of meat in a 

 dog. it was found that 30 per cent, was absorbed in the stomach, 

 while 40 per cent, passed through the pylorus as peptone, over 

 20 per cent, as undissolved or soluble protein (acid-albumin), 

 and a little more than 8 per cent, as proteose (Tobler). The 

 large proportion of peptone is noteworthy, as indicating some 

 kind of selective passage of the different digestive products 

 from the stomach into the duodenum. For the gastric contents 

 contain plenty of proteose, although only traces of peptone. 

 The total ' titratable acidity ' goes on diminishing till the third 

 or fourth hour, the proportion of free to combined acid con- 

 tinuing, nevertheless, to rise, since nearly all that is now secreted 

 remains free. In addition to a certain amount of protein, small 

 quantities of soluble and easily diffusible substances, like sugars 

 and some of the organic crystalline constituents of meat e.g., 

 kreatin may also be absorbed into the blood by the gastric 

 mucous membrane. 



The substances which reach the duodenum are : (i) The 

 greater part of the fats. The partial digestion in the stomach 

 of the envelopes and protoplasm of the cells of adipose tissue, 

 and of the protein which keeps the fat of milk in emulsion, 

 prepares the fats which are not split up by the gastric juice for 

 what is to follow in the intestine. (2) All the proteins which 

 have not been carried to the stage of peptone, and much peptone. 

 (3) All the starch and dextrins and glycogen, if any be present 

 which have not been converted into sugars, and probably a 



