the draught, causes no odors, and does not require any extra fuel.

For hotels, hospitals, or other public institutions something of greater capacity must be provided for the disposal of the garbage. To meet this demand a portable furnace has been devised, occupying about one-third of a square meter of space, with an independent chimney connection, which will destroy the waste in quantities of nearly a barrel at once. This apparatus has a garbage receptacle or retort of cast iron, cylindrical in form, with a cast-iron grate at the bottom. This retort is suspended 30 to 40 centimeters above the fire pot in the furnace, and the whole is encased in a jacket of heavy sheet iron. In operating, the retort is filled with garbage introduced through the charging door, a moderate fire is started, and the process of cremation begins. A simple arrangement of air jets, automatically actuated by the natural draught of the chimney, exhausts all the smoke and odors of the burning garbage from the retort and carries them down and through the furnace fire, so that nothing but the thoroughly purified and odorless gases, liberated by combustion, can escape into the chimney flue. Such an apparatus requires a comparatively small amount of fuel.

12

CHAPTER VII.

FOOD AND DIETING.

NOT only the health and strength of the body, but the intellectual and moral character as well, are dependent upon the nature and quantity of the food-supply. For this reason the question of food and diet is most complex, and the sanitary phase of it is not the most important one. It is, however, of sufficient importance to demand consideration in connection with general hygienic conditions, because of its relation to the welfare of man in general, and because of the dangers that arise from improper food materials, and also because of the influence upon health of excessive, as well as deficient, amounts of food.

Dr. Atwater defines food as follows: "Food is that which, when taken into the body, builds up its tissues and keeps them in repair, or which is consumed in the body to yield energy in the form of heat to keep it warm and create strength for its work."

Chemical Composition of the Body.-In order to understand the needs of the body in the shape of food to maintain its form and character, it will be necessary to consider briefly its chemical constituents. These are both organic and inorganic in their nature, composed of the following elements combined into a number of compounds Hydrogen, oxygen, nitrogen, carbon, chlorin, fluorin, sulphur, silicon, phosphorus, potassium, sodium, lithium, calcium, magnesium, and iron.

The inorganic constituents of the body are water, which comprises about two-thirds of its weight; different gases, such as oxygen, hydrogen, nitrogen, carbon dioxid, ammonia, hydrogen sulphid, and marsh gas;

salts, such as sodium chlorid, calcium phosphate (which forms more than one-half the substance of the bones), calcium carbonate and fluorid, sodium and potassium sulphate, potassium and ammonium chlorid, sodium, potassium, and magnesium phosphate, and sodium carbonate and bicarbonate; hydrochloric acid; silica; and iron.

The organic constituents may be divided into the nitrogenous and non-nitrogenous bodies, of which the nitrogenous are the most numerous. They consist of the albuminous bodies, or proteids; the albuminoid substances; certain complex bodies, such as the ferments, coloring-matters, and glucosids; and the ammonia derivatives. The non-nitrogenous bodies consist of two groups, fats and carbohydrates.

All of these various elements and chemical combinations, constituting the composition of the body, must be supplied in the food-supply in order that it may perform its normal functions and obtain energy for all of man's activities in life. Under normal physiologic conditions the amount of material absorbed from the food is about equal to that which is thrown off by the excretory organs. During the period of growth the amount absorbed exceeds the amount excreted, while in most acute diseases the amount excreted is far in excess of the amount absorbed, and, consequently, the body wastes. The body increases or diminishes in weight proportionately as the amount of material absorbed from the food is greater or less than the amount excreted. A man of average weight and activity takes about 325 grams. of dry solid matter and from 1500 to 2000 grams of water, while about 550 grams of oxygen are absorbed by the lungs per day. Of the solids taken, about 40 grams are eliminated by the intestines, and the remaining 285 grams by the other excretory organs. The oxygen taken in is also excreted by these organs, after having been burnt up; the latent or potential energy of the food being converted into kinetic energy. The body loses in

this way about one-twentieth of its weight daily, and this loss must be made up from the food ingested.

By latent or potential energy is meant the energy capable of performing work when called upon; such, for example, as resides in a suspended weight. By kinetic energy is meant energy which is doing work; such as the force exerted by the weight in falling to the ground. Heidenhain calculated that four-fifths of the total energy of the body takes the form of heat. It may be stated, therefore, that the body is a machine for converting potential energy into kinetic energy. The potential energy is supplied by the food, and the metabolism of the body converts this into the kinetic energy of heat and mechanical power.

Potential Energy in Food.-The potential energy contained in any substance is determined by ascertaining the amount of heat that is produced by its complete combustion. The potential energy contained in any substance is expressed in calories. By calories is meant the amount of heat required to warm I gram of water I degree centigrade. The amount of heat given off by the human adult body per day is equal to the heat required to warm 2,500,000 grams, or 2500 kilograms, of water I degree centigrade, and this amount of heat is generated by the body each day from the food ingested. According to König, the more common food-stuffs have values as fuel as follows:

The following general estimate of the average amount of heat and energy in 1 gram of each of the classes of nutrients has been made:

When we compare the nutrients in respect to their fuel values with their capacities for yielding heat and mechanical power, a gram of lean meat or albumin of egg is just about equivalent to 1 gram of sugar or starch, and a little over 2 grams of either would be required to equal 1 gram of fat meat or butter. These are called isodynamic values. Compared with each other, 100 grams of animal albumin are isodynamic with 52 grams of fat, 114 grams of starch, or 129 grams of dextrose; 100 grams of fat are isodynamic with 243 grams of dry flesh or 225 grams of dry syntonin.

The food is utilized in the body for the following different purposes: To form the tissues and fluids of the body; to repair the waste in the tissues; it is stored up in the body for future consumption; it is consumed as fuel, its potential energy being transformed into heat, muscular or other forms of energy; or, in being consumed, it protects the tissues or other food from consumption.

The proteid nutrients form tissue, and also serve as fuel; the fats form fatty tissue, and also serve as fuel; the carbohydrates are transformed into fat and serve as fuel.

The mechanical energy obtainable from various articles of food is dependent upon the amount of potential energy stored up in the food, which is expressed in terms of calories, and the extent to which the processes of the