THE HISTORY OF DIETETICS 419 



mentioned, he did not employ the microscope, he "was unable to work 

 out the full details of the subject. It remained for Marcello Malpighi 

 (1628-1694), of Bologna, a pioneer microscopist and one of the first 

 and greatest of histologists, in 1666 to lay down finally the essential 

 features of the minute structure and mechanism of the main glandular 

 organs as they are accepted at the present time. 



The lacteals were discovered in 1622 (published 1627) by Gaspare 

 Aselli (1581-1626), professor at Pavia, who recognized that they con- 

 veyed the chyle away from the intestine, but regarded them as empty- 

 ing into the liver, then thought to be the organ in which the food mate- 

 rials were converted into blood. The discovery of the receptaculum 

 chyli and the thoracic duct, and the connection of these with the 

 lacteals on the one hand, and the venous system on the other, was made 

 independently by Jean Pecquet (1622-1674), of Dieppe and Paris, and 

 Jan van Home (1621-1670), of Leyden, whose observations were pub- 

 lished in 1651 and 1652, respectively. 



In the ancient and middle ages, the stomach was looked upon as the 

 principal organ of digestion. The process of digestion was by some 

 (Hippocrates and others) regarded as a coction, or ir^/, (? (cooking), 

 a sort of maturation effected with the aid of heat ; by others it was con- 

 sidered as akin to putrefaction; and by still others as a mechanical 

 process. It came to be the general doctrine that the food material ab- 

 sorbed from the alimentary tract was first acted upon by the liver and 

 endowed with " natural spirits " ; in the heart, by the action on the blood 

 of the inspired air, the natural spirits were converted into "vital 

 spirits"; finally, in the brain the vital spirits were converted into 

 "animal spirits," which were then conveyed by the nerves to all parts 

 of the body. 



The beginnings of our modern knowledge of digestion can be traced 

 back to the observations of the Belgian savant Jean Baptiste van 

 Helmont (1577-1644), whose work formed a landmark in the history 

 of chemistry. He regarded the chemical activities of the body as a form 

 of fermentation, analogous to the familiar alcoholic or vinous fermenta- 

 tion; he assigned ferment action as a cause of a wide range of vital 

 processes, thus anticipating theories that at the present time are fre- 

 quently advanced. In van Helmont's view the digestion of food was 

 accomplished by fermentative action. He recognized only two stages 

 of digestion in the alimentary tract, namely, in the stomach and in the 

 duodenum; the action of the salivary glands and pancreas was not yet 

 known. Gastric digestion he regarded as being effected by a ferment 

 derived from the spleen, associated with an acid principle which was 

 necessary to its action. When the chyme passed into the duodenum the 

 acid ferment was neutralized, and the second stage of digestion was 

 effected by the bile. 



The next developments in the knowledge of digestion came from 



