DIGESTION. 



193 



Though these observations were made on the cat, evidence is 

 accumulating which goes to show that in human beings the walls 

 of the stomach exhibit constriction waves which are similar in all 

 respects to those above described. 



The Nerve Mechanism of the Stomach. The movements 

 of the stomach are to some extent independent of the nervous system, 

 though they are coordinated and regulated by it. The isolated 

 stomach of the dog and of other animals as well, if kept warm and 

 moist, will exhibit rhythmic peristaltic movements for a period vary- 

 ing from an hour to an hour and a half. Though nerve-cells and 

 fibers are present in the walls of the stomach, between the layers of 

 muscle-fibers, it is not believed that they are the immediate sources 

 of the stimulus to the contraction. The stimulus lies within the 

 muscle substance itself, and is therefore myogenic. When once 

 initiated, the contraction process propagates itself from fiber to 

 fiber. The stomach, however, receives nerve impulses from the 

 central nervous system by way of the vagi and the splanchnic nerves, 

 which determine the movements in accordance with the needs of 

 digestion.NjExperimentally it has been shown that the vipn in thr 

 augmentpr, the splanchnic the inhibitor, nerve of the stomach move- 

 me'hts/fi 1 ' Experimentally it has been shown that stimulation of the 

 peripheral end of the divided vagus augments the vigor of the peris- 

 talsis of the pyloric region and at the same time increases the con- 

 traction of the sphincter pylori muscle. Stimulation of the peripheral 

 end of the divided splanchnic is followed by inhibition of the peris- 

 talsis and a loss of tone. 



INTESTINAL DIGESTION. 



The physical and chemic changes which the alimentary principles 

 undergo in the small intestine, and which collectively constitute in- 

 testinal digestion, are probably more important and complex than 

 those taking place in the stomach, for the food is, in this situation, 

 subjected to the solvent action of the pancreatic and intestinal juices, 

 as well as to the action of the bile, each of which exerts a transforming 

 influence on one or more substances and still further prepares them 

 for absorption into the blood. 



To rightly appreciate the physiologic actions of the digestive 

 juices poured into the intestine the nature of the partially digested 

 food as it comes from the stomach must be kept in mind. This 

 consists of water, inorganic salts, acidified proteids, hemipeptones 

 and antipeptones, starch, maltose, liquefied fat, saccharose, lactose, 

 cellulose, and the indigestible portion of meats, cereals, and fruits. 

 Collectively they are known a^d^ne. As this acidified mass passes 

 "through the duodenum its cdm^KT acids excite a reflex secretion 

 13 



