284 PHYSIOLOGY OF ALIMENTATION. 



unable as such to pass through the walls of the alimentary 

 tract. They must be acted upon by the enzymes found 

 here before they can be absorbed. The starch may be ab- 

 sorbed as soon as it has been broken down to the maltose 

 stage, but most of it seems to be absorbed in the form of 

 dextrose. The glycogen is readily converted into dextrose 

 and is as rapidly absorbed. The cellulose of the food is 

 ordinarily classed as a substance which is of no use from a 

 nutritional standpoint, for it cannot be absorbed as such 

 and no enzymes are secreted by the alimentary tract which 

 can act upon it. Only the cellulose-splitting ferment (cytase) 

 contained in certain of the bacteria found in the alimentary 

 tract is able to convert cellulose into sugar, and experiment 

 shows that the amount produced in this way is exceedingly 

 small. 



Of great interest from a medical standpoint are the ex- 

 periments of HoFMEisTER, 1 who has determined the " assimila- 

 tion limits" of various carbohydrates. By the assimilation 

 limit (which is not a well-chosen term) HOFMEISTER under- 

 stands the amount of a sugar that may be administered to an 

 animal without the appearance of sugar in any form in the 

 urine. It is clear that a large number of factors play a role 

 in this complicated picture, and it is not strange that the 

 figures obtained should vary widely from each other. Never- 

 theless the general conclusions which may be drawn are 

 clear enough and are valuable in any dietary scheme in which 

 the quality and quantity of carbohydrates administered plays 

 a role. It has been found that the assimilation limit of any 

 sugar is different not only in different animals, but varies in 

 one and the same animal under different physiological con- 

 ditions, such as the rapidity with which absorption takes 

 place, the amount of sugar already present in the blood, and 

 the nutritional state of the animal as a whole. A dog that has 

 been starved for a number of days will excrete sugar in the 



1 HOFMEISTER: Arch. f. exp. Path. u. Pharm., 1889, XXV, p. 240, 

 and 1890, XXVI, p. 350. 



