Starch itself is one of this class. Tiedemann and Gmelin found that by the action of the gastric juice it was slowly converted into Dextrine, which afterwards changed into grape sugar. Both of these are very soluble. From the researches of Bouchardat and others, it appears that other fluids, as the Saliva, the secretion of Brunner's glands, and the Pancreatic juice, possess also this power of converting starch into a more soluble compound. So that if any of it escape the action of the stomach-secretion, it is probably reduced to solution and absorbed in the small intestine.
This change of starch is the first of a series of transformations, now ascertained, the ultimate result of which is its combustion and resolution into carbonic acid. Thus the nitrogenous compounds are called the _nutritive_, and the starchy materials the _calorifacient_ elements of the food. Considered as medicines, these substances belong to the division of Aliments.
6. We have already considered some few mineral substances which are absorbed by the aid of the free alkali contained in the Biliary and Pancreatic secretions.[26] The sixth kind of absorbed matters consists of some vegetable and animal products which can only be rendered soluble by a similar agency. Fats and oils, resinous matters, and some principles resembling resins, come under this head. Fats and fixed oils consist of acids, as Stearic, Margaric, and Oleic, insoluble in water, in combination with a base, Glycerine, which, when isolated, is soluble. With a free alkali such a fat forms a soluble salt, called a soap, and the base Glycerine is set free.
In Man the Bile and Pancreatic juice are discharged together into the middle of the Duodenum. The fatty matters of the food are not absorbed before they meet with these secretions. But, after they have mixed with them, a milky fluid, called chyle, is formed, which is then taken up by the lacteal absorbents. It passes thence into the Thoracic duct, meeting there with an albuminous lymph, and is discharged at length into the general circulation at the junction of the left jugular and subclavian veins.
M. Bernard, in some papers laid lately before the French Academy, states, as the result of his experiments, that the function of the Pancreatic juice is to reduce the fat to the condition of a white emulsion. He states that no milky chyle is formed when the Pancreatic ducts are tied in dogs. He considers it absolutely necessary that saccharine and albuminous matters should be absorbed by the capillaries of the Portal veins, and then pass through the liver; and believes that the sole function of the lacteals is to take up fat thus emulsified. His experiments and inferences have received the high sanction of M. Magendie.