The nutritive value of meat extracts is comparatively small; their chief value is in promoting digestion and metabolism of other foods. _Water and Metabolism._—The body consists of 530 parts of water per 1000. It is of greatest importance as a component of the tissues to assist in the exchange of nutritive substances, the discharge of the products of metabolism, the regulation of temperature, and other vital functions. If the supply of water is stopped the body will die, and it may die sooner from the deprivation of water than from starvation. A reduction in the amount of water consumed accelerates the decomposition of protein and fat to replace the water essential for the bodily functions. As the result of experiments it has been found that the average income of water is 4 pints, and the excretion is 4½ pints; so that at the lowest estimate ½ pint of water is formed in the tissues by the oxidation of hydrogen in the food and tissues; and during ordinary work it was found that 17 ounces of water was excreted daily in excess of that consumed in food and drink. The intense suffering entailed by prolonged thirst is to be accounted for by the absolute necessity for preserving the normal aqueous dilution throughout the body. Water is also essential for removing the effete materials arising from metabolism, cell growth, and other disintegration. _Chlorids._—About 15 to 18 grams of sodium chlorid (common salt) are excreted daily in the urine, and smaller quantities in the feces and perspiration. It is, therefore, a most important food. The tissues retain common salt most tenaciously, and when there is none in the food it gradually disappears from the urine. It facilitates the absorption of the protein foods and increases tissue metabolism. And, further, an insufficiency of common salt is followed by a diminution of hydrochloric acid from the gastric juice, and consequently a failure of nutrition. There can be no doubt that the hydrochloric acid of the gastric juice originates from the chlorids of the blood. On the other hand, a very large number of people consume more salt than they require. Salt is not only a food, it is a condiment, and as such it is liable to abuse. It has been estimated that from 2 to 4 grams of salt a day is sufficient, whereas most people take from 20 to 30 grams daily in one way or another. The kidneys have to excrete the excess of salt, which they seem to do in health without any difficulty; but in nephritis the kidneys do not excrete it so readily, and this may lead to a retention of salt in the body. _Iron_ is essential to the human body. It is taken into the body in the form of food, and is excreted from the body in the bile and feces. It has been estimated that typical food contains 10 mgm. of iron daily. The hemoglobin of the blood contains 0.04 per cent. of iron.