27. There is nothing more mysterious in the digestive process than the great variety of the fluids which appear essential for its completion; each of which has appropriate glands for its secretion. These fluids are, the saliva, which is formed by glands whose excretory ducts open into the mouth; and mucous matter, which results from the action of numerous follicles situated in the interior of the cheeks and palate, upon the back of the tongue, on the anterior aspect of the velum, and on the uvula; - the gastric juice, formed by glands in the stomach; and the mucus secreted by its membrane; - the "succus intestinalis," or proper juice of the duodenum and small intestines; - the bile, which being secreted in the liver, and rendered more stimulating in the gall-bladder, is afterwards carried into the duodenum; - the pancreatic juice, which is secreted in the pancreas, and carried into the duodenum along with the bile; to which may, perhaps, be added the watery liquids thrown into the intestines by the exha-lants. Were I to describe the intimate structure of the several glands and vessels which furnish these fluids, we should be led into anatomical details of tedious length, and which would be wholly unattended by practical utility.

It is, however, essential for the physiologist, as well as the practitioner, to become acquainted with the most recent account of the chemical history of these several secreted fluids.