ABSORPTION OF CARBOHYDRATES. 435 



convertible into maltose by a fresh addition of diastatic ferment after 

 complete removal of the maltose produced by the first digestion. So 

 that the failure of the ferment to convert the last portion of dextrin into 

 maltose cannot be wholly due to the stoppage of its action by the presence 

 of excess of maltose. 



There is 110 very evident reason why soluble materials like the dex- 

 trins should not be absorbed as such by the epithelial cells. The argument 

 that dextrin is not directly assimilable, because, when injected subcutane- 

 ously or intravenously, it is eliminated by the kidneys, is not valid against 

 its absorption as dextrin by the epithelial cell. For there is no reason to 

 suppose that the cell must turn it into the lymph in exactly the same 

 form in which it takes it up from the intestine ; the chances are, in fact, 

 all against such a supposition. It may be taken as probable, then, that 

 the digestive enzymes of the alimentary canal are incapable of con- 

 verting all the starch of the food into maltose, and hence into dextrose, 

 and that a portion is absorbed as dextrin, and changed into something 

 else before reaching the blood stream. 



What has been said above concerning dextrin applies also to the 

 double sugars. The intestinal juice, as we have seen, contains enzymes 

 capable of converting maltose and cane-sugar into simple sugars, and it is 

 probable that such a change does take place to a very large extent. Still 

 it cannot be concluded that the double sugars undergo complete conversion 

 before absorption. Lactose appears not to be acted upon by any of the 

 digestive enzymes, and so far as it escapes lactic acid fermentation this 

 double sugar must be absorbed by the epithelial cell unchanged. Again, 

 Brown and Heron l found that the dried mucous membrane acted much 

 more energetically on maltose than did any extract of it, which tends to 

 show that this action takes place in part within the cell. 



Eohmann 2 has also shown that not only sugar, but even starch solution 

 disappears from a Thiry-Vella fistula with considerable rapidity ; and as 

 the succus entericus possesses only an exceedingly feeble diastatic action 

 on starch, it seems that here the starch must be directly taken up by the 

 intestinal cell. Such a view is also supported by the fact that, after 

 removal of the pancreas, the secretion of which must produce the greater 

 part of the diastatic action which goes on within the intestine, one-half 

 to three-fourths of the starch of the food is still utilised. 3 Under normal 

 conditions, however, the diastatic conversion by the pancreatic juice is so 

 rapid, that it is very improbable than any appreciable portion of starch is 

 absorbed as such. 



Form in which carbohydrates reach the Hood stream. During active 

 carbohydrate absorption, traces of carbohydrates, resembling dextrin, are 

 said to be present in the blood of the portal vein, 4 but it is probable that 

 very little carbohydrate leaves the epithelial cells other than dextrose 

 or laevulose. These two sugars are capable of direct assimilation after 

 subcutaneous injection, and of forming glycogen in the liver, but no such 

 direct assimilation takes place in the case of cane-sugar or maltose. 



1 Loc. cit. 2 Arch.f. d. ges. Physiol., Bonn, 1887, Bd. xli. S. 411. 



3 Minkowski" and Abelmann (Inaug. Diss., Dorpat, 1890; Centralbl. f. Physiol., 

 Leipzig u. Wien, 1891, Bd. iv. S. 522) found, after complete extirpation of the pancreas, 

 an absorption of 57-71 per cent, of starch ; the brothers Cavazzanni (Centralbl. f. Physiol., 

 Leipzig u. Wien, 1893, Bd. vii. S. 217), under like circumstances an absorption of 47 per 

 cent. 



4 Otto, Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, 1888, Bd. xvii. S. 138 ; 

 v. Mering, Arch.f. Anat. u. Physiol., Leipzig, 1877, S. 413. 



