4 i 8 THE POPULAR SCIENCE MONTHLY 



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. rTo 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. 

 ISTo 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 Wir- 

 sung, a Bavarian (died 1643), although his pupil Maurice Hoffmann 

 contested the honor of its discovery as his own. In 1654 Francis Grlis- 

 son, 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), pub- 

 lished 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 

 1662 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 Eranciscus 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 



