These bodies have the same elements in their composition, but the hydrogen and oxygen have variable proportions - not that of water. Fats are found in large masses in some tissues, and also as fine particles suspended in many of the fluids. The fat of adipose tissue in man is a mixture of olein, palmitin and stearin, which are spoken of as the neutral fats.

The first is liquid, and the last two solid at normal temperatures, and the varying consistence of the fat of different animals depends upon the relative proportions of the solid or liquid fats.

Fats are soluble in ether and chloroform, but quite insoluble in water. When agitated in water containing an albuminous body, and an alkaline carbonate in solution, fluid fat is broken up into small particles, which remain suspended in the liquid, forming an opaque milky emulsion.

Chemically, they are regarded as ethers derived from the triatomic alcohol glycerine, C3H5(OH)3, by replacing the OH group with the radicals of the fatty acids, thus: -

Glycerine. Palmitic Acid. Tripalmitin. Water

' C8H5(OH)3 + 3(C16H3202) = C3H5(C16H3102)3 + 3H20.

Under the influence of certain ferments they separate into glycerine and the fatty acid, uniting with the necessary elements of water.

When the neutral fats are boiled with alkaline solutions they are similarly decomposed, and uniting with the elements of water, form glycerine and fatty acids. The glycerine is thus set free, but the fatty acid combines with the alkaline metal to form a soluble soap. An insoluble soap may be obtained by substituting lead or lime, etc., for the alkali.

This splitting up of the neutral fats, stearin, palmitin and olein into sodium stearate, palmitate, or oleate goes on during digestion, and is said to be useful in aiding the absorption of fatty matters.