Page:Popular Science Monthly Volume 83.djvu/427

Rh form in 1897. For this work Pavloff received the Nobel prize in 1904.

The discovery of pancreatic secretin by William Maddock Bayliss and Ernest Henry Starling, announced in 1904, opened up an entirely new field of knowledge, that of the action of the so-called hormones as inciters of secretory activity carried to the points of action by the circulation.

The introduction of the X-ray made available a new and fertile method of studying the movements of the digestive organs; one of the earliest and most prolific workers in this field has been an American, Walter Bradford Cannon, professor of physiology at Harvard, whose contributions on this subject date from 1899.

The main basis of dietetics rests in the chemistry of food and nutrition. This knowledge could not be developed until the science of chemistry entered upon its renaissance, which occurred much later than the birth of modern anatomy, physiology and physics. The discovery of oxygen in 1774 opened the way to a rapid development of chemical knowledge, just as Harvey's discovery of the circulation a century and a half before had been the starting point for physiology.

As has been the case with many other discoveries, the effective discovery of oxygen had been anticipated long previously by work that had fallen into oblivion. In 1668 a young Englishman at Oxford, John Mayow (1645-1679), published a remarkable work in which he argued that the atmosphere contains, as he styled it, an "igneo-aereal" or "nitro-aereal" principle which by combining with combustible ("sulphureous") substances constitutes the process of combustion; that this principle is imparted to the blood by the respiratory activities; that the union of this principle, carried in the blood, with combustible material in the muscles gives rise to muscular action and is a source of animal heat. Though this theory was soon forgotten, it was a remarkable presentation of the doctrine of oxidation (including body oxidation as the source of animal energy), and anticipated by a century the discovery of oxygen.

In 1774 oxygen was independently discovered by Joseph Priestley (1733-1804), an English clergyman, and by Karl Wilhelm Scheele (1742-1786), of Sweden. It was Antoine Laurent Lavoisier (1743-1794), of Paris, however, who grasped the real significance of this discovery, and by his researches, published from 1775, overthrew the false though fruitful phlogistic theory of heat that had dominated chemistry for a century, and showed the true nature of combustion and the properties of oxygen.

Lavoisier was followed by a number of brilliant investigators, who rapidly laid down the great foundations of chemical science. The beginnings of organic chemistry may be traced to some of these early workers; Lavoisier, for instance, showed that organic compounds are