Animal nucleic acid Plant nucleic acid Phosphoric acid Phosphoric acid Hexose (levulose) Pentose (_d_-ribose) Guanine Guanine Adenine Adenine Cytosine Cytosine Thymine Uracil The structure of the plant nucleic acid may be represented by the following formula: OH | O=P--O--carbohydrate-guanine group | O | O=P--O--carbohydrate-adenine group | O | O=P--O--carbohydrate-uracil group | O | O=P--O--carbohydrate-cytosine group | OH That this is probably a correct representation of the general arrangement in this compound, is indicated by the fact that by different methods of hydrolysis it is possible to split off either the purine and pyrimidine bases, leaving a carbohydrate ester of phosphoric acid; or the phosphoric acid, leaving carbohydrate combinations with the nitrogenous bases. Nucleic acid, prepared from animal glands which contain large proportions of it, is a white powder, which is insoluble in water, but when moistened forms a slimy mass. It is almost insoluble in alcohol, but dissolves readily in alkaline solutions, forming a colloidal solution which readily gelatinizes (see chapter on Colloids). Solutions of nucleic acids are optically active, probably because of the carbohydrate constituents. From their structure and properties, it is apparent that nucleic acids are on the border line between carbohydrates, plant amines, and proteins. They undoubtedly play an important part, both in cell-growth and in the synthesis of proteins from carbohydrates and ammonium compounds. References BARGER, GEO.--"The Simpler Natural Bases," 215 pages, _Monographs_ on Biochemistry, London, 1914. FISCHER, E.--"Untersuchungen in der Puringruppe, 1882-1906," 608 pages, Berlin, 1907. HENRY, T. A.--"The Plant Alkaloids," 466 pages, Philadelphia, 1913. JONES, W.--"The Nucleic Acids," 118 pages, _Monographs_ on Biochemistry, London, 1914. PICTET, A.--"La Constitution Chimique des Alcaloides Vegetaux," 421 pages, Paris, 1897 (2d ed.). VAUGHAN, V. C. and NOVY, F. G.--"Ptomaines, Leucomaines, Toxins and Antitoxins," 604 pages, Philadelphia, 1896, (3d ed.). WINTERSTEIN, E. and TRIER, G.--"Die Alkaloide," 340 pages, Berlin, 1910. CHAPTER XIII PROTEINS