. Elements of human physiology. Physiology. THE MATERIAL BASIS OF THE BODY 49 Fats are insoluble in water, but soluble in ether and in hot alcohol. When boiled with alkaline solutions, they are split up with the formation of glycerin and a compound of the fatty acid with the alkali, which is called a soap. The alkaline soaps are soluble in water. In the fats of milk (butter) we hnd lower acids of the fatty series, such as butyric, caijrylic, and caproic acids, combined with glycerin. Acetic acid is also a member of the fatty acid series. It occurs in the body as an amino-acid, glycine. Lecithi
. Elements of human physiology. Physiology. THE MATERIAL BASIS OF THE BODY 49 Fats are insoluble in water, but soluble in ether and in hot alcohol. When boiled with alkaline solutions, they are split up with the formation of glycerin and a compound of the fatty acid with the alkali, which is called a soap. The alkaline soaps are soluble in water. In the fats of milk (butter) we hnd lower acids of the fatty series, such as butyric, caijrylic, and caproic acids, combined with glycerin. Acetic acid is also a member of the fatty acid series. It occurs in the body as an amino-acid, glycine. Lecithin.—This substance is a wax-like body which is universally distributed in the organism, and is found in espe- cially large quantities in the white matter of nerves and of the spinal cord. It may be regarded as a compound of a molecule of glycerin with two of stearic acid, one of phos- phoric acid, and a molecule of a nitrogenous base, cholin. Its composition is represented by the following formula : ((,0,). [^ ^"^ (0-aH,—N(CH3)30H. Lecithin is miscible in all proportions in ether, alcohol, and fats. It swells up in water, of which it can imbibe a large quantity. Cholesterin may be considered here although it does not belong to the group of fats. Like lecithin it is found wherever protoplasm is present and seems to be an essential con- Fiu. Cholesterin crystals. stituent of every living cell. It is a monatomic alcohol (C2,;H,). It is easily soluble in ether or hot alcohol. From the latter it is deposited on cooling in typical plate-like 4. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Starling, Ernest Henry, 1866-1927. Chicago : W. T. Keener
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