Page:Popular Science Monthly Volume 83.djvu/428

424 composed mainly of carbon, hydrogen and oxygen, and sometimes nitrogen.

The foundation and elaboration of organic chemistry was mainly the great achievement of the illustrious chemist Justus Liebig (18031873). After studying chemistry at Paris under Gay-Lussac, he was professor of chemistry at Giessen 1824-1852, and at Munich from 1853 until his death in 1873. About 1837 he began epoch-making investigations of physiologic and organic chemistry, and in works published from 1840 he laid down the main lines of our knowledge of the chemistry of food and nutrition. He first, for instance, sharply differentiated the foodstuffs albumen, fat and carbohydrate, and recognized the tissue-forming function of albumins and the heat-producing properties of fats and carbohydrates.

Since the time of Liebig many workers have brought our knowledge of the chemistry of food to its present state. Among important investigations of this character now being actively prosecuted are those on the molecular structure of the complex foodstuffs, such as the studies of Emil Fischer, Emil Abderhalden and others on the proteins. Some of the sugars have been artificially synthesized, and a beginning has been made even on the proteins.

Crude attempts at food analysis date back for centuries, as in connection with governmental measures to prevent adulteration of foods and beverages. In the modern era George Pearson, of England, in 1795 reported an analysis of potatoes; in 1805, Einhoff analyses of potatoes and rye. Eeliable analyses of milk were reported by Peligot in 1836, and of feeding stuffs and milk by Boussingault and Le Bel 1836-1839. From about 1840, through the work of Liebig a great impetus was given to food analysis; and with the further advances of chemistry came the development of reliable analytic methods and the accumulation of data. From about 1860 the standard methods of food analysis now employed were developed by Wilhelm Henneberg (1825-1890), of the agricultural experiment station at Weende, near Göttingen; these methods soon came into general use and have greatly facilitated and systematized this line of work.

Possibly the earliest analyses of food made in the United States were of some cereals by C. U. Shepherd published in 1844. Analyses of various foods were published by Salisbury in 1848, Beck in 1848-1849, Emmons in 1849, Jackson in 1857. One of the most prolific workers in this field in this country was Atwater, who, employing the Weende methods, made analyses of maize in 1869, and commenced an extended series of analyses of fish and other foods in 1877.

Dietary studies—investigations of the amounts of foodstuffs actually consumed by different classes of people under various conditions—furnish an important part of the data underlying the science of dietetics. Among the earliest investigations of this sort were those conducted by