Page:Popular Science Monthly Volume 83.djvu/422

418 and medieval eras of medical thought, there was very little of abiding verity or value that contributed to our present rational knowledge of the subject. On the contrary, the professional mind was thoroughly indoctrinated with erroneous ideas which retarded the acceptance of correct conceptions and have not even yet been eradicated.

The science of dietetics is a composite subject, uniting a number of rather independent branches of knowledge, such as the chemistry of food, the processes of digestion, the physiology of metabolism, etc., the development of which may be separately considered. The beginnings of our scientific knowledge of these subjects may be traced back to the seventeenth century, soon after the discovery of the circulation of the blood by William Harvey (1578-1667), announced in 1628, opened the way to the development of scientific physiology. No great progress, however, was made for nearly two centuries, and the main foundations of our knowledge of these subjects were laid down in the second quarter of the nineteenth century.

The development of our knowledge of the physiology of digestion will be first considered.

A knowledge of the mechanism of glandular secretion in general is prerequisite to an understanding of the origin of the digestive fluids. No adequate conception of the structure and function of glands was possible prior to the discovery of the circulation and the use of the microscope. When these conditions were fulfilled the physiology' of glandular secretion was quickly worked out. At first, for instance, it was not even known that, except for the liver and kidneys, the glands possessed ducts. The main steps in the evolution of our knowledge of glandular action were about as follows:

In 1643 the duct of the pancreas was first described by Georg Wirsung, a Bavarian (died 1643), although his pupil Maurice Hoffmann contested the honor of its discovery as his own. In 1654 Francis Glisson, an Englishman (1597-1677), published an important work on the liver, in which he touched upon the mechanism of the secretion of the bile. In 1656 Thomas Wharton, an Englishman (1610-1673), published an account of the duct of the submaxillary gland. In 1662 Lorenzo Bellini, of Florence (1643-1704), at the early age of 19 years, described certain portions of the uriniferous tubules of the kidney. In 1663 also Nicolas Stensen, or Steno, a Dane (1638-1686), described the ducts of the parotid and other glands. The names of these observers have ever since been attached to the structures which they discovered.

About this time Franciscus Sylvius, Stensen's instructor at Leyden, drew a general distinction between conglomerate glands, possessing secretory ducts, such as ordinary secreting glands, and conglobate glands, such as the lymphatic glands. Stensen, from his researches on the salivary and other glands, came close to an adequate conception of the process of glandular secretion; but as, like the other observers just