THE FUNCTIONS OF THE DIGESTIVE ORGANS. 507 



kneaded in the true sense of the word. The innervation of the musculature 

 of the stomach is partly provided by the vagus and partly by the sym- 

 patheticus. Since even the extirpated stomach contracts spontaneously, 

 it has been assumed that the ganglion-cells in the walls of the stomach can 

 cause this action. 1 



After the chyme is formed, the stomach has fulfilled its task. The 

 pylorus then opens and the chyme enters the duodenum. This trans- 

 ference does not take place all at once. The time that the food remains 

 in the stomach depends upon a number of factors. Purely physical 

 conditions, such as the size of the food particles and the chemical nature 

 of the contents of the stomach, both have an effect. 2 



Frequently we hear of a foodstuff being easily digestible or difficultly 

 so without its being perfectly clear just what is meant by the term. 

 As a matter of fact, it depends upon two factors. A food may be readily 

 digestible, i.e., it can be readily acted upon by the ferments in the stomach, 

 and yet appeal to us, according to its entire behavior, as difficultly diges- 

 tible. This is due to the fact that although it may be easy for the ferments 

 to act upon a food, still it may be converted into chyme only with consider- 

 able difficulty. The readiness with which a food may be converted into 

 chyme should always be considered with regard to its digestibility. Diges- 

 tion experiments in a test-tube cannot decide this. Many contradictions 

 in theory and practice are to be traced to this point. Our present knowl- 

 edge concerning the digestibility of various foods in the human stomach is 

 still very vague. 



As just mentioned, the stomach is not emptied all at once. It begins 

 to be emptied very soon after the beginning of digestive activity. Thus 

 when a dog is fed with meat, the first products of digestion appear in the 

 duodenum after a few minutes. The stomach is emptied intermit- 

 tently. 3 In feeding 100 grams of meat to a dog weighing 7 to 8 kilograms, 

 all the chyme was emptied in the course of 2J hours. It is difficult to get 

 a correct idea of the time spent by the food in the stomach from such 

 experiments. They are often very contradictory. We shall understand 

 immediately why this is so, when we are told that Pawlow has proved 

 that normally the opening and closing of the pylorus are regulated by the 

 duodenum. If hydrochloric acid, or gastric juice, is constantly intro- 

 duced into the duodenum through a fistula, a soda solution placed in the 

 stomach will be retained during the whole course of the experiment. The 

 period which normally follows the opening and closing of the pylorus 



1 Concerning the literature, see E. H. Starling: Ergeb. Physiol. (Asher and Spiro) Jg. I, 

 Abt. 2, 446 (1902). Extensive studies on the functions of the muscles of birds have 

 been made by Mangold: Pfluger's Arch. Ill, 163 (1906). 



3 Cf. Moritz: Z. Biol. 42, 565 (1901). von Mering: Kongress f. innere Med. Berlin, 

 1877 and Wiesbaden, 1893. A. Hirsch: Zentr. klin. Med. 47, 993 (1892). 



3 Cf. Ludwig Tobler: Z. physiol. Chem. 45, 185 (1905). 



