4 2o THE POPULAR SCIENCE MONTHLY 



Franciscus Sylvius (Frangois 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 dis- 

 coveries, Sylvius attached an exaggerated importance to the digestive 

 action of the saliva, and held that digestion in the stomach was accom- 

 plished 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 Eegner de Graaf (1641-1673), of 

 Holland, published the results of investigations on the pancreatic secre- 

 tion 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 effer- 

 vescence, 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 (con- 

 glomerate) 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, pub- 

 lished 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 



