and his associates in Bonn, by Zuntz in Berlin, by Tschudnovski, Pashutin, and others in St. Petersburg, by Tigerstedt in Sweden, and by many others.
The energy exchanges of the organism have a fundamental bearing in dietetics, since the heat output of the body under different conditions determines the caloric requirements of the diet. The apparatus used to investigate these exchanges, the respiration calorimeter, besides measuring the respiratory products after the manner of Pettenkofer's apparatus, determines with great accuracy the amount of heat given off by the subject. In its perfected form this mechanism is a marvel of complexity, elaborateness, and delicacy, requiring much labor and ample resources for its construction and operation.
Some imperfect calorimetric studies on animals and man were published by Russian observers from 1884. Max Rubner (1854-) was the first to conduct a successful and elaborate series of calorimetric observations on animals. He was educated at Munich under Toit; professor at Marburg 1885-1891; at Berlin from 1891, succeeding Koch as Director of the Hygienic Institute. His studies were begun about 1889, and his results published in full in 1902. He demonstrated that the law of the conservation of energy holds good for animals; and he has laid down principles fundamental in this branch of physiology and of the utmost importance in dietetics.
The most elaborate calorimetric investigations ever carried out have been those prosecuted in this country since 1892 by Wilbur Olin Atwater (1844—1907) and his associates and successors. Atwater studied at Munich under Voit, and derived some of his ideas from Rubner. Professor of chemistry at Wesleyan University, Middletown, Connecticut, from 1873 until his death, he devoted his whole life to investigations concerning food and nutrition. In 1892, with the assistance of the physicist Rosa, he began the construction at Wesleyan University of a respiration calorimeter large enough to accommodate a human subject. This apparatus underwent gradual improvement until finally direct determinations of the oxygen exchanges were, for the first time on a large scale, carried out. The work was jointly supported by Wesleyan University, the Storrs (Connecticut) Agricultural Experiment Station, the United States Department of Agriculture, and (later) the Carnegie Institution. With this apparatus an elaborate series of researches was carried out from 1892 to 1907, the results of which must stand as classical. After Atwater's death in 1907, the original apparatus was removed to Washington and installed in the Department of Agriculture, where it is now in operation; while his successor Francis Gano Benedict under a grant from the Carnegie Institution is continuing the research with an equipment constructed in Boston.
Other investigators have since taken up this line of work, and impor-
