Page:Popular Science Monthly Volume 83.djvu/424

420 Franciscus Sylvius (François de la Boe, or Dubois, 1614-1672), the professor of medicine at Leyden, who founded the iatro-chemical school and exerted a powerful influence as a teacher and expositor of the chemical philosophy of his time. Sylvius also attributed many of the vital processes to fermentative action; but he confused effervescence (such as occurs on adding acid to carbonate) with fermentation, and looked upon effervescence as the type of these processes. Sylvius had knowledge of two secretions, salivary and pancreatic, unknown to van Helmont.

The observations of Wharton and Stensen (published 1656 and 1662) had clarified the salivary secretion. Impressed with these discoveries, Sylvius attached an exaggerated importance to the digestive action of the saliva, and held that digestion in the stomach was accomplished much more by swallowed saliva than by any ferment of gastric origin. This view persisted for a long time.

The second stage of digestion, that taking place in the duodenum, according to Sylvius was effected by the conjoint action of the bile and the recently discovered pancreatic juice. Wirsung in 1643 had described the pancreatic duct; and in 1664 Regner de Graaf (1641-1673), of Holland, published the results of investigations on the pancreatic secretion carried out while he was a student at Leyden under Sylvius. De Graaf obtained pure pancreatic juice from dogs through quills inserted into the pancreatic duct. He fell into the error, however, of regarding it as acid; and he held, in accordance with Sylvius's theory of effervescence, that the effervescence supposed to be produced by the mixture of this acid juice with the salts of the bile was in some way associated with duodenal digestion.

In 1677, Johann Conrad Peyer (1653-1712), a Swiss, published a description of certain glandular structures discovered by him and since known as Peyer's patches. He decided that these were secretory (conglomerate) rather than lymphatic (conglobate) glands, and believed their secretion had digestive properties, active in the lower ileum at a point where the pancreatic juice must become exhausted.

In 1683, Johann Conrad Brunner (1653-1727), of Germany, published the results of experiments which he had made in exsecting the pancreas and ligating the pancreatic duct in dogs. As the dogs did not manifest any disturbance of digestion or nutrition, he argued that the importance attached by Sylvius and de Graaf to pancreatic digestion was unfounded. Brunner also showed that the pancreatic juice was not acid. In 1687 he described the duodenal glands, since known by his name, and attributed digestive properties to their secretion.

In consequence of the doubt brought by the discoveries of Peyer and Brunner, belief in pancreatic digestion waned, and for a long time the view prevailed that the stomach was the chief seat of digestion. In the latter part of the seventeenth century, two opposing theories as to the