The same distinction is made between oils and fats for animal products as has been made for the vegetable preparations further on. An animal fat remains solid or semisolid at the ordinary temperature of the living room. An animal oil, on the other hand, is one which at ordinary temperature is a liquid. Animal oils, as a rule, are not used for edible purposes directly, but are used to some extent in cooking, and to a large extent as medicinal food. Inasmuch as these oils are used for medicinal food purposes, those which are most important in this use may be very properly described in this manual. As these oils are derived both from sea and land animals they are often conveniently divided into marine animal oils and terrestrial animal oils. There is also a marked difference as a rule between the oils of marine origin and those of terrestrial origin. The oils of marine origin, as a rule, have a very high iodin number while the animal oils of terrestrial origin have an iodin number not much greater than the fats from which they are derived. This distinction corresponds somewhat closely to those vegetable oils which belong to the drying and non-drying variety. The iodin number represents the percentage of iodin absorbed by a unit weight of substance. If one gram of an oil absorb 0.67 gram of iodin, the iodin number is 67. The marine oils correspond to the dry vegetable oils and the terrestrial oils to the non-drying vegetable oils. While this difference is one which is marked, it does not always exist in each individual case.

MARINE ANIMAL OILS.

The marine animal oils may be conveniently divided into fish oils, liver oils, and blubber oils. Of these the liver oils are the most important from an edible point of view or a medicinal edible point of view. The fish oil and blubber oil are used chiefly for illuminating and other technical purposes. Fish Oils. These are obtained by rendering from all parts of a fish where fat exists. The herring, sardine, salmon, and the menhaden are the fish. which are chiefly used for getting oil of this kind. The fish oils have very much improved in quality since the steamer has taken the place of the sail boat for gathering the fish. During the days of the sail boat the fish were often kept for ten days after seining before they were brought ashore. The decomposition which took place would naturally affect the oil. At the present day the steamers fishing close to the shores deliver their products much more frequently, often the same day they are caught, and thus a better quality of oil is produced. In this country menhaden is the chief fish used. for obtaining oil. The scientific name of menhaden is Brevoortia tyrannus. These fish appear in enormous quantities around the Atlantic coast from May until November. It is estimated that nearly one-half million tons have

been taken of these fish during a season. Menhaden oil is rarely if ever used for edible purposes. It is used principally in the leather trade and sometimes in the adulteration of cod liver oil made in Newfoundland.

Sardine Oil.-Sardine oil is principally prepared in Japan from the Japan sardine (Clupea sardinus). It is not used to any extent for edible purposes. It is also prepared to some extent in the boiling of sardines in France preparatory to packing in oil.

Salmon Oil.-This oil is obtained in large quantities on the Pacific coast. It is one of the fish oils which has an agreeable odor and taste and, therefore, can be used for edible purposes. It has a specific gravity at 15 degrees of about .926 and its iodin number is about 160.

Cod Liver Oil.-The most important of all the animal oils for food purposes is the oil which is obtained from the liver of the cod (Gadus callarias). Cod liver oil is valuable for food purposes not on account of its odor and taste, which are usually quite disagreeable, but by reason of the specific effect which it is often said to exercise in cases of emaciation and general disorder of the functional activities of the body. It is a food or medicine, whichever it may be best called, which is highly prized in tuberculosis and similar diseases. The oil is chiefly prepared in the Loffoden Islands. Different classes of oil are prepared which are differentiated chiefly by their color, the lighter the color the higher the quality of the oil. The chemical composition of cod liver oil is extremely complex, many different kinds of substances having been found in it by various authorities. The probability is that many of these supposed substances are only mixtures of others. Yet it cannot be denied that the number of chemical compounds occurring in cod liver oil is very much greater than that which occurs in ordinary oils. Both the medicinal and food values of the oil are often attributed to these bodies which occur in minute quantities.

Properties.-Cod liver oil at 15 degrees has a specific gravity of .922. Its iodin number varies very greatly but is always high, ranging from 150 to 180. Its refractive index is also very high, namely 1.47.

An important constituent of cod liver oil is cholesterol. Cod liver oil contains naturally a small quantity of iodin and this natural compound of iodin is one of the properties to which much of its medicinal virtue has been attributed. The quantity present is extremely minute, and probably never exceeds .002 of one percent.

Adulteration of Cod Liver Oil.-Owing to its increasing price cod liver oil has been subjected to many forms of adulteration. The chief adulteration consists in the admixture of fish liver oil of lower quality or the use of blubber oil. Seal and whale oils have been used very extensively in the adulteration of cod liver oil. Japan fish oil and, in fact, all other fish oils which are of a character not to disguise the properties of cod liver oil have been used.

It is evident that it is with extreme difficulty that the presence of these adulterants can be detected, especially if they are used in small quantities. The only certain method of guarantee of the purity of a cod liver oil is in the proper inspection and control of the manufacturing works. The livers of many other kinds of fish are employed in the manufacture of cod liver oil, but the other varieties have little value as compared with the cod liver oil itself and they are probably used almost exclusively in the adulteration of the genuine article. The Norwegian cod fish gives a much better character of oil than those coming from the Atlantic coast of America. In fact the latter product. is of little medicinal food value and is used chiefly in the leather trade.

Blubber Oil.-Blubber oil includes the oils made from seals, whales, turtles, etc., and is used exclusively for technical purposes, unless surreptitiously placed in cod liver oil as an adulterant.

PART IV.

MILK AND MILK PRODUCTS AND

OLEOMARGARINE.

MILK.

Limitation of Name.-By the term "milk," unless qualified in some way, is meant a lacteal secretion of the healthy cow, free of colostrum and of standard quality. If the milk of other mammals is meant the name of the class of animal is used in connection with the term, such as ewe's milk, goat's milk, etc. Milk is one of the most important articles of commerce and, by reason of its composition, high nutritive character, and easy digestibility, it is not only the natural food of infants but a most important food for children and adults. It is also an indispensible food in many, if not most, cases of disease where nutrition is impaired. In some cases life may often be sustained over a critical period by the use of milk as a food where other forms of food would fail of digestion and prove injurious instead of beneficial.

The United States standard for milk is found in Appendix A.

Average Composition of Milk.-Perhaps there is no food substance which has been subjected to so many and such severe analytical tests as milk. Hundreds of thousands of analyses have been made in all civilized countries, not only of the milk of the individual cow but of herds of greater or less size.

There is a great variation in the composition of milk in different breeds of cattle and also in different individuals of the same breed. For instance, the Holstein breed of cattle affords a milk with a very low content of fat, sometimes as low as 3.25 percent, and in individual cases lower. On the other hand the Jersey breed of cattle affords a milk of a very high content of fat, sometimes reaching as high as 6 percent, and in individual cases very much higher. The content of the nitrogenous element in milk is more stable than that of fat and the common content of casein in milk ranges from 2 to 3 percent. The sugar in the milk is usually the complementary substance with the fat, diminishing in relative proportions as the fat increases and vice versa. The average content of sugar in cow's milk is approximately 4 percent. The content of mineral substances in milk is also quite constant, being about 0.70. The ash contains the phosphoric acid which is one of the essential food components of milk. A milk of fair average quality contains 12 percent of solids and 88 percent of water. This is an expression for milk during the