In common with the carbohydrates, fats are composed of carbon, hydrogen, and oxygen, but in contradistinction to them contain more carbon and less oxygen, for which reason a given quantity of fat on burning will produce 2 1/4 times as much heat. In the human body and bodies of animals they are found in large quantities in bone marrow, adipose tissue, and milk, whilst in plants they are most commonly found in seeds, e.g. nuts, Unseed, etc. Body fat is a mixture of three fats, stearin, palmitin, and olein, and on account of the low temperature at which the last-named becomes solid, viz. 5° C. (41° F.), the contents of the fat cells of the adipose tissue are fluid during life. Fats and oils are identical in composition, only differing in their melting-points. Fats are insoluble in water, although their component parts, viz. fatty acids and glycerine, are soluble. Hence in the body during digestion they are split up into these substances and so absorbed. Milk contains varying proportions of fat - cow's milk 3 1/2 to 4 per cent., while whale's milk contains as much as 43 per cent., and this is an interesting illustration of adaptation when one remembers the heat-producing powers of fat.