650 Transactions of the American Institute. 



limited to particular species of food. The different elements of 

 food are digested in different parts of the alimentary canal, by the 

 agency of those different digestive fluids, and by their action the 

 various ingredients of the alimentary mass are successively reduced 

 to a fluid condition, so as to be taken up by the blood vessels, and 

 the absorbent vessels of the intestinal mucous membrane, thus to 

 be introduced into the general circulation. 



The action which is exerted upon the food by the digestive fluids 

 is by no means that of a simple chemical solution. It is an actual 

 transformation, by means of which the ingredients of the food are 

 altered in character at the same moment they undergo the process 

 of liquefaction. The active agent in producing this change, in every 

 instance, is an organic principle entering as an ingredient into the 

 digestive fluids, and which, by coming into contact with the food, 

 exerts upon it a catalytic action, and transforms its ingi'edients into 

 other substances. The newly-formed substances resulting from this 

 cataljtic action, are absorbed by the vessels, and finally mingled 

 with the general current of the circulation as blood, by which the 

 system is nourished and sustained. The food, in order to be 

 digested, is acted upon by no less than five different digestive 

 fluids: First, the saliva in the cavity of the mouth; second, the 

 gastric juice in the stomach; third, the bile from the liver; fouilh, 

 the pancreatic fluid from the pancreas; fifth, the intestinal secre- 

 tions from the follicles in the intesthial canal. The saliva acts 

 upon the starchy (carbon and hydrogen) elements of the food, con- 

 verting them into sugar. This action, though not so marked as the 

 action of the secretions further on in the alimentary canal, is one 

 of no little importance; and, doubtless, some of the forms of indi- 

 gestion which the physician has to combat in his practice, are a 

 result of the useless expenditure and waste of this secretion in the 

 habit of smoking, and more particularly the habit, almost peculiar 

 to this country, that of chewing tobacco. The gastinc juice acts 

 upon albuminoid elements, like the gluten in bread and casein in 

 milk. In a healthy human adult the quantity of gastric juice 

 secreted in twenty-four hours probably ranges from ten to twenty 

 pints; its maximum, in an hour, under favorable circumstances, is 

 not less than from six to eight pints. Of the action of the bile in 

 the process of digestion, much has yet to be established, but that it 

 exercises a stimulating influence upon the absorbents is fully proven. 

 The secretion from follicles of the intestinal canal continue, and 

 complete the digestion of the starchy elements of the food. 



