Solid neutral fats, such as suet, lard, and spermaceti, also liquid non-volatile oils, such as olive oil, and sperm oil, are classed together as chemical fats. They are composed of carbon, oxygen, and hydrogen, but do not contain any nitrogen. When a fat is treated with an alkali, the fatty acid unites with the alkaline base, making a soap, and glycerine is set free. Fats are distinct from other food elements which increase the weight, and warmth of the body, such as the sugars, starches, and cellulose, these being carbohydrates, which are more affected by heat than the fats; but the latter when cooked, at a high temperature, which is kept up, undergo some disintegration, and a free fatty acid is liberated; this is apt to disagree with delicate stomachs. Meat to be fried should be plunged suddenly into a deep pan of nearly boiling fat, pure olive oil, or dripping, or butter. The intense heat produces an instant coagulation of the proteids (resembling white of egg) on the surface, and forms a protective crust. It is supposed that the greater digestibility of cold fats over hot fats is because the fatty acid then unites again with glycerine to form a neutral fat free from acid on cooling. Carbon enters the body for fuel in fat, starch, and sugar, and quits it as carbonic dioxide.

Lean persons who wish to gain fat should eat but little lean meat, whilst taking freely of butter, potatoes, white bread, and plain pastry, if easily digested; they should live in warm well-ventilated rooms, and refrain from much active out-door exercise. Furthermore there is much truth in the maxim, "to eat little and often will make a man fat".

For contributing fat to lean persons the Banana cure is now popular in America. This consists of eating scarcely anything besides baked Bananas, which not only add weight, but at the same time recruit the nervous energies of body and mind. But those who advocate cooked Bananas are emphatic in condemning "them raw as dangerous and unwholesome. Banana flour is found valuable in cases of stomach inflammation, and in typhoid lever, as it can be retained, if suitably prepared, when other forms of the appropriate foods are rejected. Sir Henry Stanley, the famous explorer, wrote concerning this Banana flour, "if only its virtues were publicly known, I cannot doubt that it would be largely consumed in Europe. For infants, persons of feeble digestion, and dyspeptics, the flour, properly prepared, would be in universal demand. During my two attacks of gastritis, a light gruel of such flour mixed with milk, was the only matter that could be digested."- It contains twenty per cent of proteids, and sixty-eight per cent of carbohydrates. The Banana is always pure, and never tainted by grubs: its outer skin protects the fruit entirely from contamination. Experts say that the Banana, like the Medlar, can scarcely be in too ripe a stage for eating.

The British Medical Journal (1904), teaches that Bananas should not come to table before their skin has turned black in places, whilst their pulp is at the same time slightly discoloured.

Fish-oils, notably that from the cod's liver, are more easily digested than ordinary fats, but are not so highly organized. The next most readily borne, and assimilated is bacon fat, either hot, as rashers, or of cold boiled bacon, which serves a much better purpose for building up the bodily tissues. Then comes cream, a natural emulsion; likewise butter. For children another capital combination of fat may be supplied by toffee, this being made of sugar, butter, and sometimes a portion of treacle. Butter in such a shape is especially agreeable to the young stomach; and most of the toffee-sugar occurs as "invert," which is particularly easy of digestion.

For lean, or wasted patients one of the simplest means of enriching the diet is by adding to it a certain quantity of rich new milk, two, or three pints a day, besides the ordinary nourishments; also "croutes au coulis," or gravy fingers, afford fat in a useful and palatable form. "Take several slices of stale bread, choosing them not too much dried up, chop off the crusts, cut the crumb into neat finger lengths, dip them rapidly in, and out of a' basin of cold milk, drain them, brush them over with white of egg, and dredge them thickly with flour. Melt three table-spoonfuls of clarified beef-dripping in a small saucepan, and bring it to the boil, lower the fingers separately into this, and cook them until crisp, and brown. Build them up as a small pyramid in the centre of a heated dish, and pour over it a teaspoonful or two of strong beef gravy, or of a flavoured brown sauce".

All children need a liberal allowance of heat-producing food, but most of them have a dislike of fat; therefore they naturally crave for sugar as a substitute. Thus their desire for sweets is the cry of nature for what she wants; and this voice of nature should be obeyed; nevertheless fatty foods are good for prurigo, and other skin troubles of children.

Dr. R. Hutchison, in a recent lecture before the National Health Society of London, "had a good word to say for Margerine as physiologically equal to Butter; than which latter substance there is no food stuff of higher value! " His emphatic opinion is that there is too much starch, and too little fat in the national diet system, and that therefore a stunted race of the working classes is growing up. Dripping used to be given liberally to the children of the poor; bread and dripping was the staple article of their food; but this has now given place to cheap jams, which do not possess the same nutritive value as the said fatty substance, (whereto the homely bloater likewise may be profitably compared), these things being supplemented with lentils, oatmeal, haricot beans, and a certain amount of animal food; for it cannot be doubted that together with the carbohydrates, such as starches, sweets, cream, etc., an adequate allowance of nitrogenous nutriment in the form of fresh meat, eggs, casein of cheese, gluten of cereals, and vegetable nitrogens, helps materially to lay on fat; indeed, is essential for the purpose.