72 DIGESTION OF CAEBOHYDEATES. 



it does not appear that they can metamorphose other carbohydrates into 

 this body, we may infer, as would indeed seem probable, considering the 

 nature of the food of many of them, that they can digest woody fibre. 

 The digestive apparatus of man, however, can not exert such a power. 



Neither does it appear that gum undergoes either digestion or absorp- 

 Digestion of ti n ' I n artificial experiments it also resists the action of di- 

 gum. gestive fluids, and is not changed when present during the 



fermentation of other bodies, even though its exposure thereto be contin- 

 ued for several days. Administered to animals, it is almost entirely 

 voided with the excrement. Thus Boussingault, having given to a duck 

 fifty grammes of gum-arabic, obtained forty-six grammes from the ex- 

 crements in nine hours. In an experiment upon an old rabbit, to which, 

 with a diet of cabbage-leaves, ten grammes of gum-arabic were daily given 

 by Lehmann, the gum being administered in solution in water by injec- 

 tion into the stomach, no trace whatever of gum could be detected in 

 the urine, none in the chyle of the thoracic duct, and none in the blood, 

 but it was easily enough recognized in the excrement. From this he 

 infers that the preparations of gum, which are such favorite medicines 

 with some physicians, yield to the animal organism only an extremely 

 small quantity of material of a nature to support the respiratory process, 

 and that their uses, if they are of any use, can be merely negative in 

 acute diseases. 



Of the carbohydrates, starch is perhaps the most important, occurring 

 Digestion of as ^ does in abundance in vegetable food. It can not be made 

 starch. use O f j n ^he system without fifst being transmuted into dex- 

 trine, sugar, and eventually lactic acid, these changes being greatly ex- 

 pedited if it has been previously prepared by boiling in water, or other 

 equivalent operations of cooking. The saliva commences the action, 

 which in man is even prolonged in the stomach, and in the herbivora still 

 more decisively in the paunch, in birds in the crop. On gaining the stom- 

 ach, the farther transmutation of the starch is arrested by the gastric 

 juice, but after reaching the duodenum it is resumed with greater energy 

 than ever, under the influence of the pancreatic juice. Reaching the ile- 

 um, the intestinal juice continues the action, though with less vigor. In 

 this passage to the large intestine, the starch is gradually assuming the 

 condition of dextrine and sugar, the former substance passing into the 

 latter with such facility that it can only be recognized transiently. 

 Doubtless the sugar thus arising is in great part directly absorbed, though 

 some, before the ccecum is reached, is transmuted into lactic acid, and oth- 

 er portions, after passing through the ileo-coecal valve, into butyric acid. 



From what has been observed respecting starch, it may be inferred how 

 Digestion of important sugar is, since through the condition of sugar alone 

 sugar. i s starch available for the uses of the system. It is to be rec- 



