. Essentials of biology presented in problems. Biology. 356 DIGESTION AND ABSORPTION cavity, called the pulp cavity, corresponds to the cavity containing marrow in bones. In life it contains living material — the blood vessels, nerves, and cells which build up the bony part of the tooth. The bulk of the hard part of the tooth consists of a limy material called dentine. Outside of this is a very hard substance called enamel; this substance, the hardest in all the body, is thickest on the exposed surface or crown of the tooth. Each tooth is held in its place in the jawbone by a thin layer of bon
. Essentials of biology presented in problems. Biology. 356 DIGESTION AND ABSORPTION cavity, called the pulp cavity, corresponds to the cavity containing marrow in bones. In life it contains living material — the blood vessels, nerves, and cells which build up the bony part of the tooth. The bulk of the hard part of the tooth consists of a limy material called dentine. Outside of this is a very hard substance called enamel; this substance, the hardest in all the body, is thickest on the exposed surface or crown of the tooth. Each tooth is held in its place in the jawbone by a thin layer of bony substance called cement. Problem XL VI. How foods are chemically prepared for ab- sorption into the hlood. {Laboratory Manual, Proh. XZ VI.) (a) In the mouth. (b) In the stomach. (o) In the small intestine. Salivary Glands. — We are all familiar with the substance called saliva which acts as a lubricant in the mouth. Saliva is manufactured in the cells of three pairs of glands which empty into the mouth, and which are called, according to their position, the parotid (under the ear), the sub- maxillary (under the jawbone), and the sublingual (under the tongue). Digestion of Starch.—If we col- lect some saliva in a test tube, add to it a little starch paste, place the tube containing the mixtine for a few minutes in tepid water, and then test with Fehling's solution, we shall find grape sugar present. Careful tests of the starch paste and of the saliva made separately will usually show no grape sugar in either. If another test be made for grape sugar, in a test tube containing starch paste, saliva, and a few drops of any weak acid, the starch will be found not to have changed. The digestion of starch to grape sugar is caused by the presence in the saliva of an enzyme, or digestive ferment. You will remember that starch in the growing corn grain was changed to grape sugar. A B Experiment showing non-osmosis of starch in tube A, and osmosis of Bugar in tube Please note
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