The action of the stomach in digestion, appears, therefore, so far as our actual knowledge extends, a purely catalytic fermentative action; one in which the active excitant is an organic substance (pepsine), secreted by the mucous surface, and whose properties are developed by the presence of muriatic acid, which is secreted at the same time. The new products into which the food, fibrine, albumen, gluten, starch, oils, sugar, etc., are converted, and which collectively constitute the white uniform pulp, termed by physiologists chyme, have not been made the subject of accurate chemical researches. In the mouth the mass of nutritive material is acted on by a liquid which is secreted by the salivary glands, the saliva. It is alkaline, and holds in solution not one per cent. of solid matter, which contains some carbonate of soda and common salt, admixed mucous, and a peculiar organic body, termed salivary matter. This last substance is soluble in water; its solution is not coagulated by heat, nor precipitated by tincture of galls, corrosive sublimate, acetate of lead, nor by acids. The pancreas, so similar in structure to the salivary glands, has a different secretion; it contains no salivary matter, but albumen and some salts; it is generally slightly acid. _Composition of the Bile._—The precise part which this remarkable secretion performs in the animal economy is not yet fully known; it has been the subject of repeated and accurate chemical examination, although, from the facility with which its elements are transferred into other bodies, by the action of the reagents employed, every succeeding analysis has led to different results. _The Coloring matter of the Bile._—is present during health but in small quantity, but in disease it sometimes accumulates so as to form solid masses. When pure, it is a reddish-yellow powder, which is scarcely soluble in water or in alcohol, but dissolves easily in a solution of caustic potash. This solution is of a clear yellow color, but when exposed to the air it becomes deep green, absorbing oxygen. This change is remarkably produced by nitric acid, and it is indeed the reaction by which the presence of the bile in the serum of the blood, in the skin, in the urine, and eyes, etc., may be shown in cases of jaundice. _Chyle and Lymph._—The nutritive materials extracted from the food by the absorbing vessels of the intestines, is thrown into the thoracic duct, where it meets with another fluid, which is transmitted to the same vessel from all parts of the body by the colorless veins or lymphatics. The fluid from the intestines is termed chyle; that from the body is generally termed lymph. It is the mixture of these that has alone been examined, for the vessels which carry either separately are too minute to allow of the extraction of their contents in a pure form.