Butter consists in mechanically concentrated milk fat, with about 1/2% each of lactose and protein, traces of lactic acid, some salts from the milk as well as common salt added. For practical purposes, it may be considered as 90% fat and, hence, yields calories amounting to 8 - 8.5 times its weight in grams. Since the absorption of fats is inverse to the melting point, butter fat is better absorbed than any other in common use excepting salad oils, the waste being 1 - 6% under ordinary conditions. Its palatability renders it especially available in wasting diseases, leanness, etc., and, conversely, its high yield of calories in proportion to its bulk renders it especially prone to cause superalimentation and the simpler forms of obesity. 15 grams is commonly considered a rather meagre serving yet this amount at each meal represents a net assimilation of about 350 calories.

Skimmed milk contains small quantities of fat but is, in regard to protein and lactose, as nutritious as whole milk. Separator milk contains only about 1/10% of fat.

Buttermilk is the residue of sour cream, after the butter has been removed by churning. It contains about 3% of protein, 1/2% of fat and 4 - 4.5% of carbohydrate. Its acidity is about that of a decinormal solution or a little less, owing to the bacterial conversion of part of the lactose into lactic acid. While highly lauded it should be remembered that it is really nothing but sour, skimmed milk and that there are many instances in which the introduction of an excess of lactic acid and of a culture of lactic acid bacteria is objectionable. It may be used occasionally even in infant feeding, especially when it is desired to overcome virulent putrefactive bacteria.

Koumys is a milk in which lactic acid and alcohol have been developed by fermentation and was originally used (probably on account of spontaneous development of saprophytes, in the leather sacks used to hold mare's milk) by the nomadic tribes of the steppes of south-eastern Europe and western Asia. On account of this origin, the term applies strictly to mare's milk, which is better adapted to this form of fermentation by the relatively high percentage of lactose and low percentage of fat, than is cow's milk. When prepared from mare's milk of a breed producing milk especially rich in lactose, the alcohol amounts to 2% or more. As ordinarily prepared extemporaneously, from cow's milk, with brewer's or compressed yeast, koumys contains only about 1% of alcohol. At ordinary temperatures, the yeast should be allowed to act for about 24 hours, or until a marked lactic acid reaction and slight effervescence are noted. While it may be preserved by bottling, it is perhaps best used soon after preparation.

For practical purposes, koumys may be considered as an alcoholic buttermilk, available in conditions of saprophytosis with excessive fat and protein decomposition, hence often in gastric cancer. It is often available in typhoid and other fevers, but should be used according to the taste of the patient and with due regard to the potential disadvantage of a sour, alcoholic beverage. It is relatively less nutritious than milk, bottled koumys sometimes containing not over half the proportion of organic nutrients in milk.

Curd and whey are, respectively, the casein with contained water and salts with other ingredients caught in the curd, and the milk minus the coagulated casein. The coagulation may be produced by souring, as in the preparation of cottage or Dutch cheese or by rennet, as in ordinary cheese manufacture. Coagulation by acidification is usually due to spontaneous, bacterial formation of lactic acid but may be produced by adding lemon juice, etc. So, too, rennet is sometimes allowed to act upon sour milk. Either curd or whey or both may be used as a food, variously flavored with salt, salt and pepper, or sweetened and spiced. Whey contains 1% of protein in the form of an albumin not coagulated by rennet.

Junket is prepared by sweetening milk with sugar, adding a little light wine or liquor, if desired, curdling with rennet and spicing. Many invalids would prefer unsweetened soft curd and whey with salt.

Cheese curd is commonly considered indigestible and it undoubtedly is somewhat so, on account of its toughness, but it must be remembered that its delicious taste and the difficulty of obtaining it, unless in the immediate vicinity of factories, tempts to overeating. If well masticated or grated, it is not especially indigestible.

Cheese consists of pressed curd, cured by the more or less digestive action of various bacteria. During this action, the lactose is more or less decomposed, forming lactic acid and even alcohol, carbon dioxid, etc., which evaporate. Some decompo-sition of proteins also takes place. Lard or other fats are sometimes rubbed into cheese and the quantity of fat also depends upon whether cream, cream and milk, ordinary milk or skimmed milk is used as a source of curds. Different kinds of cheese vary considerably in their content of organic nutrients but most contain 20 - 25% of protein, 25 - 40% of fat and from a trace up to 2 or 3% of carbohydrate. The flavor of cheese is to some extent due to foreign ingredients as sage, savory, etc., and somewhat to different strains of microorganisms producing different chemic products. Thus the flavor and the air spaces of Swiss cheese are due mainly to colon bacillus action; a special strain of bacteria causes the flavor of Camembert: and Roquefort owes its flavor to pen-icillium developing in bread crumbs with which the curd is rubbed up. Limburger is characterized by an excess of strictly putrefactive processes.

While cheese is almost purin-free, the various organized ferments contained, as well as decomposition products and the physical state of the mass, render it somewhat difficult of digestion and prone to occasion alimentary saprophytosis. It may be partially sterilized and the products of germ life already present may be partially removed by toasting and almost entirely so by cooking to form a Welch rabbit (rare-bit is a far-fetched and historically incorrect etymology). The bad repute of this dish is due partly to the tendency to return to a stringy mass but more particularly to the excess of beer, mustard and other condiments, to its use at irregular hours instead of at meal time and to concomitant excesses in eating and drinking. When prepared with plenty of milk or as a cheese custard and eaten at meal time, Welch rabbit is usually well digested by persons of ordinary strength of digestion.

Custards are used mainly by English speaking peoples, and by the French, the Germans having no word for combinations of egg and milk. Whether raw, baked or boiled, they may be variously flavored so as to take the place of meats or desserts and are highly nutritious. The reputation of egg-nog, a raw custard reinforced with whisky or brandy is exaggerated. The raw egg albumin is not so likely to be assimilated as the cooked and the alcoholic liquor is of doubtful utility in many instances. However, while possessed of no miraculous tonic powers, and representing only the sum of the nutrients and calories of its ingredients, egg-nog is useful in many conditions in which ordinary foods are not well taken, even the liquor stimulating the digestive secretion.