It is a well known fact that different degrees of heat applied to all substances produce entirely different substances. Some changes are for the better, or are harmless, while other products are injurious. Eugene Christian says, "All foods raised to a temperature beyond that of the boiling point are in process of being changed into ash, which is poison in proportion to the amount of heat applied," thus a slice of bread toasted crisp all the way through only requires a little more heat to reduce it to ashes, being worse than valueless as food. Yet the ash, like most poisons, produces a craving for more of it, as is apparent from the demand for well-browned food of all kinds. When vegetables or fruits are boiled, as already explained, the mineral elements which nature has prepared in exact proportion for the best purposes are changed and often set entirely free from their combinations, undoing the work of nature. Some materials as sugar, fats, and starch, having no proteid or but very little, require a higher degree of heat than that of boiling to injure them for food or to greatly change their composition whence, for convenience, they may be boiled or raised to that degree of temperature for many purposes, however, sugar is injured by acid of fruit in boiling with it, and at 4000 of heat loses most of its sweet taste, becoming caramel, which is often used by cooks as a brown coloring; starch exposed to the same temperature becomes grape sugar and fats change into fatty acids that are injurious to the mucous membrane of the digestive organs. Because of this unstable condition of chemical properties of food when acted upon by heat, each improvement in the methods of intensifying heat makes a more imperative demand that it should be scientifically applied for hygienic cooking.

Besides the many chemical changes to be considered in all elements subjected to heat it must not be forgotten that the body building cells in food are delicate, sensitive, living things that may be impaired or killed, hence must be treated with care and thought amounting to respect of life.

When heat is applied to food it should be in a systematic manner, and be kept constant, or be changed gradually to avoid shocks after the cell is once revivified by the warmth. A simmering pot of food loses much of its flavor if its liquor is replenished by a supply of cold water instead of with water of the same temperature. Its nutritive value is also decreased, as the shock is weakening to the cells. The chick in an egg develops more perfectly and has a greater power of endurance, or tenacity to life, when the temperature is kept uniform than if exposed to extremes of heat and cold. The nuclei of the cells should have as favorable conditions before quickening or being quickened to reproduce the cells of human tissue, hence the next essential in scientific cooking after a low degree of heat is established, is that of steady heat that can be easily and perfectly controlled.

Food materials being of different natures - the vegetable cell being invested with a cellulose coat while the animal cell is without it - and the effect of combinations being varied for nutritive value, taste, appearance, and convenience, heat cannot be applied in the same manner to all kinds of substances. The whole kernels of grain or dry seeds that have lost moisture for preservation must regain it slowly by long soaking and be gently raised to the desired temperature to soften the cellulose covering without toughening it, as in boiling, while meat must have the outer cells seared and sacrificed by quick intense heat to prevent the escape of the juices of the interior cells during the process of slow cooking, unless soup is being made. Bread and pastry, to retain the shape by forming a crust, as well as to arouse the action of the enclosed gases, must be subjected to quite a high degree of heat at first until the inside is heated through and raised to the point of coagulation, which is not quite to the boiling point, after which the temperature is lowered for slow, steady baking. The crust is as valueless for nutrition as the skin of an apple, but the enclosed cells are perfect in vitality, so far as the life principle is concerned, even though some combinations of pastry are not easily digested. Ground or broken kernels of grain, as cereals, including rice, must be dropped into water at the full boiling point, as the cold cereals lower the temperature immediately, allowing the gluten to dissolve in the water unless it coagulates quickly. After the first coagulation, by slight simmering, the cooking must be . slow and steady. Ripe fruits and green vegetables may be softened and cooked, without being boiled at 2000, fruits being sweetened when soft, but most of them serve a better purpose and are more palatable in the natural state.

Some of the present cooking already fulfills the requirements of scientific living, but it is more accidental than intentional. With all good cooks food is known to be more savory if slowly simmered or roasted, while Ralston and other standard authorities upon hygienic cooking, as Sarah Tyson Rorer, in the "Ladies' Home Journal," recognize the value of the living cell and sound a warning note against cooking food until it is dead. The Ralston Health Club also advocates baking light bread two hours, hence, from necessity, the heat must be low enough to save the life of the nuclei of the cells within the loaves. Thus some of the most stable articles of diet are saved from the devitalizing effect of high degrees of heat by those who follow the system, besides it is quite common to cook many things in a double boiler to prevent burning.

The biscuit had always been condemned by hy-gienists, but although not so healthful as unfired or light bread, it serves a purpose as a quickly prepared food, for emergencies. The inside coagulates at about 200°, and as it is the custom of the careful housewife to open the oven door at this stage, allowing the biscuits to stand in the heat a few minutes longer to finish baking, all of the laws of cooking are fulfilled, thus many instances might be given where the vitality of food is retained in the present cooking, even though it may easily be lost in the same food by carelessness. By pains and knowledge every article of diet may be wholesome and nourishing instead of a large part of each day's rations being waste, leaving the system depleted in the effort- to cast it off.