Much care is also requisite to prevent imperfect mastication of this kind of food. Orange peel and the skins and stones of cherries, plums and grapes are wholly indigestible, and often cause serious mischief when swallowed. Cucumbers, green potatoes, green fruit of all kinds should be wholly discarded from the diet. DRINKS. Water in some form is more essential to our existence than any of the solid aliments we have yet considered, and is next in importance, in the performance of the vital process, to the air we breathe. Water enters into the formation of all the various tissues of the body, and constitutes a very large proportion of the human system. The blood contains about eighty per cent., the flesh about seventy-six per cent., of water; and of the entire human body, at least seventy-five per cent., or three-fourths of its weight, is water. The most important purposes in the animal economy are accomplished through this medium. In the blood, the solid vital elements are transported by the medium of water from one part of the body to another, in a form and condition to promote the vital changes which are constantly taking place. In exhalation, secretion and absorption, the presence of water is indispensable. It acts as a solvent of various alimentary substances, and thus assists the stomach in the act of digestion; though when taken in large quantities immediately after eating it dilutes the gastric juice and hinders digestion. Water enters more or less largely into the composition of all alimentary substances, and is taken into the stomach in a pure state, or forms the principal part of the various kinds of drinks in use. Water is unquestionably the natural drink of adults, and meets the wants of the body more perfectly than any of the artificial liquids which are regarded as improvements on water. Whenever a man is left to the cravings of instinct, unbiased by a vicious appetite, he invariably resorts to water as the natural means to quench his thirst, cool his system, and invigorate his wasting strength. When we say that water is the only fitting drink for man’s daily and habitual use, we are sustained by the facts of the case. Water is the only liquid which is necessary to the formation, development and support of his frame; it is equal to all the exigencies of thirst, for the relief of present inconvenience, and of dilution, by mixing with his blood and other fluids, to prevent further sufferings and disease. DIGESTIBILITY OF ALIMENTARY SUBSTANCES.