< IBSORPTIOb ( >/■ ( '- / RBOH ) PR. 1 TES. 435 
convertible into maltose by a fresh addition of diastatic ferment after 
complete removal of the maltose produced by the first digestion. ^ So 
ili.it the failure of the fermenl to convert the lasl portion of dextrin into 
maltose c mnot be wholly due to the stoppage of its action by the presence 
of excess of malto 
There is no 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 thi epithelial cell. For there is no reason to 
Buppose 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 1 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.- 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 'hi which carbohydrates reach fJt<: blood 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. tit. - Arch. f. <1 . ges. Physiol., Bonn, 1887, Bd. xli. S. 411. 
3 Minkowski and Abelniann (Iuaug. Diss., Dorpat, 1890; Centralbl. f. Physiol., 
Leipzig u. Wien, 1-91, 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. «. d. Fortschr. d. XL ier-i 'h em,., Wiesbaden, 1888, Bd. xvii. S. 138 ; 
v. Muring. Arch. f. Anal. u. Physiol., Leipzig, 1877, S. 413. 
