288 DIGESTION. 



substance to be nutritive, it must be capable of being 

 assimilated to the blood ; and to find its way into the 

 blood, it must, if insoluble, be digestible by the gastric 

 fluid or some other secretion in the intestinal canal. There 

 is, therefore, thus far, a necessary connection between the 

 digestibility of a substance and its power of affording 

 nutriment. 



Those portions of food which are liquid when taken into 

 the stomach, or which are easily soluble in the fluids 

 therein, are probably at once absorbed by the blood- 

 vessels in the mucous membrane of the stomach. Magen- 

 die's experiments, and better still, those of Dr. Beaumont, 

 have proved this quick absorption of water, wine, weak 

 saline solutions, and the like ; that they are absorbed 

 without manifest change by the digestive fluid, and that, 

 generally, the water of such liquid food as soups is 

 absorbed at once, so that the substances suspended in it 

 are concentrated into a thicker material, like the chyme 

 from solid food, before the digestive fluid acts upon them. 



The action of the gastric fluid on the several kinds of solid 

 food has been studied in various ways. In the earliest 

 experiments, perforated metallic and glass tubes, filled 

 with the alimentary substances, were introduced into the 

 stomachs of animals, and after the lapse of a certain time 

 withdrawn, to observe the condition of the contained sub- 

 stances ; but such experiments are fallacious, because 

 gastric fluid has not ready access to the food. A better 

 method was practised in a series of experiments by Tiede- 

 mann and Gmelin, who fed dogs with different substances, 

 and killed them in a certain number of hours afterwards. 

 But the results they obtained are of less interest than 

 those of the experiments of Dr. Beaumont on his patient, 

 St. Martin, and of Dr. Grosse, who had the power of 

 vomiting at will. 



Dr. Beaumont's observations show, that the process of 

 digestion in the stomach, during health, takes place so 



