Page:Popular Science Monthly Volume 83.djvu/429

Rh Liebig in 1810; by Beneke in England in 1851; and in this country by John Stanton Gould in 1852 and Atwater in 188G. Since then many such studies have been made and a large amount of information collected.

A knowledge of the processes of metabolism forms another component of the foundations of dietetics.

Probably the earliest real metabolism studies were prosecuted by Sanctorius (1561-1636), who published his results in 1614. Sitting in a chair suspended from steelyards, he observed the changes in weight from eating and from the loss of insensible perspiration.

Theories of the source of animal heat were presented from the early days of physiology. Van Helmont held that animal heat was generated by fermentation of the blood in the heart. Sylvius believed it to be produced by the supposed effervescence resulting from the mixture of venous blood with acid chyle. Mayow in 1668 anticipated the modern view that the body energy is derived from oxidation in the tissues; but his views were soon forgotten. Toward the end of the seventeenth century these chemical theories were largely superseded by the physical view that animal heat is generated by the friction of the blood in the capillaries. It was not until after the discovery of oxygen that our present conceptions of the part played by oxidation as the source of animal energy were founded by Lavoisier.

The general outlines of our knowledge of metabolism were formulated by Liebig, the details being worked out by numerous subsequent investigators, many of them under his personal influence. In this way, chiefly since 1850, an extensive mass of data on this subject has been accumulated. The earliest metabolism study appears to have been one by Lehmann, made in 1839. The study of the metabolism of nitrogen is a comparatively simple matter, and has been an easy and frequent subject for investigation.

The determination of the exchanges of carbon and hydrogen is a much more difficult matter, involving the collection of the products of respiration and requiring elaborate apparatus and an amount of labor rarely available. Early respiration experiments with animals were made by Boussingault about 1844, Bidder and Schmidt in 1847-1850, and Regnault and Reiset in 1849; and with man by Barral in 1847-1848, and Hildesheim in 1856.

A most extensive and accurate series of investigations was conducted by Max von Pettenkofer (1818-1901) and, especially, Carl von Voit (1831-1908), in the Physiological Institute at Munich with the respiration apparatus constructed by Pettenkofer about 1860. Animals and men were made the subjects of extended observation with this apparatus from 1861 to 1867, and principles of fundamental importance were established by these classical researches.

Other important studies of metabolism were prosecuted by Pflüger