DIGESTION. 93 



expands to allow them to pass out, and it closes again to 

 confine the residue for further preparation. 



28. The knowledge of these and other interesting and 

 instructive facts has been obtained by actual observation ; 

 the workings of the stomach of a living human being have 

 been laid open to view and examined the result of a re- 

 markable accident. Alexis St. Martin, a Canadian voyageur, 

 received a gun-shot wound which laid open his stomach, 

 and which, in healing, left a permanent orifice nearly an 

 inch in diameter. Through this opening the observer 

 could watch the progress of digestion, and experiment with 

 different articles of food. Since that occurrence, artificial 

 openings into the stomach of the inferior animals have 

 been repeatedly made, so that the facts of stomach-digestion 

 are very well ascertained and verified. 



29. Gastric Digestion. What portions of the food 

 are digested in the stomach ? It was formerly thought 

 that all the great changes of digestion were wrought here, 

 but later investigation has taught us better. We now know 

 that the first change in digestion takes place in the mouth, in 

 the partial conversion of starch into sugar. We also know 

 that, of the three organic food principles (considered in 

 Chapter IV.) two the fats and the sugars are but slightly 

 affected by the stomach ; but that its action is confined to 

 that third and very important class, from which the tissues 

 are renewed, the albuminoids. A few articles need no 

 preparation before entering the system, as water, salt, and 

 grape-sugar. These are rapidly taken up by the blood- 

 vessels of the stomach, which everywhere underlie its 

 mucous membrane in an intricate and most delicate net- 

 work. In this way the function of absorption begins. 



30. The albuminoid substances are speedily attacked and 



28. How has the knowledge and the workings of the stomach been ascertained ? 

 St. Martin? How else? 



29. What was formerly thought. ? What do we now know ? What else do we 

 now know ? Water, salt, and sugar? Absorption ? 



30. Albuminose? The process ? Chyme? 



