154 PHYSIOLOGY CHAP. 



suceedent dans les organes digestifs durant 1'acte de digestion," led 

 to the publication of two important monographs, one by Leuret and 

 Lassaigne (1825), the other by Tiedemann and Gmelin (1826), in 

 which the entire process of digestion was for the first time 

 submitted to an experimental criterion. The work of the two 

 German authorities in particular must be regarded as the starting- 

 point of subsequent experimental researches, since they established 

 the foundations on which the whole of the modern doctrine of 

 digestion rests. 



In collecting the gastric juice, Tiedemann and Gmelin intro- 

 duced a modification of the method pursued by Reaumur and 

 Spallanzani, since they caused dogs to swallow insoluble bodies in 

 order to stimulate the walls of the stomach. They then killed the 

 animals, collected the juice secreted, and studied its solvent action 

 on food in vitro. A few years later (1833) Beaumont published 

 his experiments on the Canadian trapper, Alexis St. Martin, who, 

 in consequence of an accident, had a large gastric fistula, which 

 made him a convenient subject for the study of the phenomena of 

 natural digestion. And shortly after (1834) Eberle published his 

 discovery of artificial gastric juice obtained from extract of mucous 

 membrane, with which numerous series of artificial digestions in 

 vitro were carried out by himself, by Job. Miiller, Schwann, 

 Wasmann, Vogel, Valentin, etc. This return to Spallanzani's 

 method indicates a marked progress in the positive knowledge of 

 the nature and properties of the digestive process. 



Among the more complete monographs on digestion, of special 

 historical interest, are those of Blondlot (1843), Frerichs (1846), 

 and Bidder and Schmidt (1852). 



II. The Digestive System, which is a canal extending from 

 the mouth to the anus, has on an average a length of about nine 

 metres. The part that lies in the head, neck, and thorax measures 

 from the mouth to the cardiac orifice of the stomach some 38 to 

 46 cm. ; the remainder, situated between the abdomen and the 

 pelvis, is almost twenty times as long. The former includes the 

 mouth, the pharynx, and the oesophagus ; the latter the stomach, 

 the small intestine, and the large intestine. This anatomical 

 division clearly indicates the lines we must follow in studying the 

 mechanical and chemical changes in the food-stuffs introduced into 

 the digestive canal. 



The first 'secretion which the food encounters is the saliva 

 poured into the buccal cavity, in a daily quantity (according to 

 Bidder and Schmidt) of more than 1500 c.c. Prima digestio fit in 

 ore, as the ancients phrased it. At first sight it appears as if the 

 saliva, secreted in such abundance, must have a highly important 

 chemical function. Everything, on the contrary, indicates that 

 the operations effected on the food in the mouth are mainly of a 

 mechanical character, 



