150 DIGESTION. 



or vexation, will take away the appetite and interfere with diges- 

 tion. Any nervous impression of this kind, occurring at the com- 

 mencement of digestion, seems moreover to produce some change 

 which has a lasting effect upon the process; for it is very often 

 noticed that when any annoyance, hurry, or anxiety occurs soon 

 after the food has been taken, though it may last only for a few 

 moments, the digestive process is not only liable to be suspended 

 for the time, but to be permanently disturbed during the entire 

 day. In order that digestion, therefore, may go on properly in the 

 stomach, food must be taken only when the appetite demands it ; 

 it should also be thoroughly masticated at the outset ; and, finally, 

 both mind and body, particularly during the commencement of the 

 process, should be free from any unusual or disagreeable excite- 

 ment. 



INTESTINAL JUICES, AND THE DIGESTION OF SUGAR AND STARCH. 

 From the stomach, those portions of the food which have not 

 already suffered digestion pass into the third division of the ali- 

 mentary canal, viz., the small intestine. As already mentioned, it 

 is only the albuminous matters which are digested in the stomach. 

 Cane sugar, it is true, is slowly converted by the gastric juice, out- 

 side the body, into glucose. We have found that ten grains of 

 cane sugar, dissolved in 3ss of gastric juice, give traces of glucose 

 at the end of two hours ; and in three hours, the quantity of this 

 substance is considerable. It cannot be shown, however, that the 

 gastric juice exerts this effect on sugar during ordinary digestion. 

 If pure sugar cane be given to a dog with a gastric fistula, while 

 digestion of meat is going on, it disappears in from two to three 

 hours, without any glucose being detected in the fluids withdrawn 

 from the stomach. It is, therefore, either directly absorbed under 

 the form of cane sugar, or passes, little by little, into the duodenum, 

 where the intestinal fluids at once convert it into glucose. 



It is equally certain that starchy matters are not digested in the 

 stomach, but pass unchanged into the small intestine. Here they 

 meet with the mixed intestinal fluids, which act at once upon the 

 starch, and convert it rapidly into sugar. The intestinal fluids, 

 taken from the duodenum of a recently killed dog, exert this 

 transforming action upon starch with the greatest promptitude, if 

 mixed with it in a test-tube, and kept at the temperature of 100 F. 

 Starch is converted into sugar by this means much more rapidly 

 and certainly than by the saliva ; and experiment shows that the 



