82 SALTS AND GASES OF THE INTESTINE. 



Successive tions of the tube, but in the same region, in different parts 

 tmSt^ouoi! of tne mass ' its exterior ma 7 te alkaline, its interior acid, or 

 the intestine, the converse. The acidity which has been imparted by the 

 gastric juice seems generally to have disappeared some time before the 

 large intestine is reached. In this an alkaline reaction is observed. The 

 causes of this prolonged acidity are very various. In part it depends on 

 the nature of the food, in part upon the gastric juice, as has just been 

 stated, and in part upon the production of lactic, butyric, and other acids. 

 The resinous ingredients of the bile may be detected as far as the lower 

 extremity of the ileum. Glucose, originating in the action of the pancre- 

 atic and intestinal juices on starch, may be recognized throughout the 

 whole length of the canal, but that which has been introduced in the 

 food seems to be absorbed in the stomach itself; thus, in milk-fed ani- 

 mals, sugar does not appear to descend beyond the jejunum. 'The trans- 

 mutation and reabsorption of biliary matter commences in the small in- 

 testine and proceeds continuously, so that by the time the middle of that 

 portion of the tube is reached, half the bile is gone. 



Since the intestinal absorbents can only take up a definite proportion 

 of fat, it might be expected, as is really the case, that after an unusually 

 fatty diet, fat substances will be found in the excrement. Indeed, a cer- 

 tain small proportion always so occurs. 



Of the salt substances usually occurring in the food, most disappear 

 Salts of the in- during their passage through the intestine, and hence but lit- 

 testine. tie is found in the faeces ; more particularly is this the case 



with those of a very soluble kind. Of the sulphates and chlorides of the 

 food, not even a trace may occur in the excrement. If these substances 

 should not be required for the uses of the system, they are promptly re- 

 moved by the kidneys, and in the same manner are disposed of any ab- 

 normal salt substances which may have been purposely administered, as, 

 for instance, iodide of potassium. 



The gaseous contents of the intestine originate in part from the air 

 Gases of the that has been introduced during the mastication of the food, in 

 intestine. p ar f r0 m fermentative processes occurring after certain articles 

 have been used which are only imperfectly digested, and in part from the 

 endosmosis of gas from the blood through the walls of the intestinal cap- 

 illaries. As compared with atmospheric air, though the composition 

 must necessarily be very various, the intestinal gas shows a great excess 

 of carbonic acid and nitrogen, a diminution and sometimes even a total 

 absence of oxygen, the presence of pure hydrogen, and of its carburets 

 and sulphurets. The quantity of this latter gas is less than might be 

 expected from its odor, and, as would be anticipated from the circum- 

 stances, the accumulation of gas is much more abundant in the large than 

 in the small intestine. 



