The fats or oils are compounds greatly important in the nutrition of man. There are many individual fats, those known in common life as tallow, lard, butter, and oils, such as linseed and cottonseed oils, being mixtures of three or more of these.

When any finely ground foodstuff, either vegetable or animal, is submitted to the leaching action of ether, chloroform, or certain other liquids, several compounds are taken into solution, the main and important ones being fats or oils. These bodies make up the chief portion of such an extract from seeds, while material so derived from other vegetable materials also contains a considerable amount of wax, chlorophyll, and other substances. Tables that show the composition of foods have a column which is sometimes designated "ether-extract," and sometimes "fats or oils." The former is the more accurate term, because the compounds which it is the intention to describe are often no more than half fats or oils. The real value of the "ether-extract" from different foods is partly determined, therefore, by its source. When it is all oil, or nearly so, it is worth much more for use by the animal than when it is made up to quite an extent of other bodies.

82. Fats In Grains And Seeds

The proportions of fat or oil in foods vary within wide limits. In general, seeds and their by-products contain more than the stem and leaves, the differences in the percentages of actual oil being greater than is indicated by the ether-extract. But little is found in the dry matter of roots and tubers. Among the cereal grains and other more common farm seeds, corn and oats show the largest amounts, the proportion in dry matter being from five to six in one hundred, while wheat, barley, rye, peas, and rice contain much smaller percentages, wheat having about 2 per cent, and rice sometimes not over one-fifth of 1 per cent. Agricultural seeds that are especially oleaginous are cottonseed, flaxseed, sunflower seeds, and the seeds of many species belonging to the mustard family, such as rape. Peanuts, coconuts, and palm nuts are also very rich in oil. The average percentages in these seeds and nuts are approximately as given below:

Table XVIII Oil In Certain Seeds

The oils from all the above are important commercial products, being used in a great variety of ways in human foods and in the arts. In many cases, the refuse from this extraction goes back to the farm as food for cattle. This is especially true of linseed and cottonseed.