30 
Proceedings of Royal Society of Edinburgh. [sess. 
to find very different degrees of development in different organisms, 
and even in the same organism, as regards the different substances 
to he digested. Thus cholera appears to digest its proteids by 
means of enzymes, but the faculty of digesting the carbohydrates 
appears still to reside in the protoplasm. How far the process is 
carried out in each case by means of enzymes, and how far, directly, 
by the protoplasm, must be decided by experiment. Even in the 
alimentary canal the process is not carried out by ferments alone. 
Starch is there converted into equal quantities of maltose and 
dextrine, and the latter is unaffected by the further action of the 
enzymes; yet as neither of these bodies is absorbed as such, the 
portal vein containing the carbohydrates only in the form of 
dextrose, these must undergo their further changes at the hands of 
the cells. In a similar way lactose and cane sugar are split up by an 
inversive ferment into equal quantities of dextrose and levulose, and 
the further transformation of the latter is evidently to be referred 
directly to the protoplasm.* The greater part of the albumen is 
undoubtedly peptonised before being absorbed, yet, as Yoit and 
Bauer f have shown, a part may undergo direct absorption. More 
recent experiments, in cases of artificial anus, where the influence 
of the ferments from the upper straits of the canal was completely 
excluded, have shown that egg albumen undergoes direct absorp- 
tion; and since egg albumen is excreted by the kidneys as a foreign 
body, the disintegration and rebuilding up which is necessary for 
its assimilation must be attributed purely to cellular action. In all 
probability the cells lining the alimentary tract perform a much larger 
part of the preliminary processes of digestion than is at present 
conceded to them. 
An enzyme is accordingly to be looked upon as a function which 
has undergone a high degree of differentiation, indeed, as a property 
which is able to exist and act apart from the protoplasm. As each 
organism is adapted to special conditions, we should expect the 
enzymes also to act best under these conditions. It has already been 
stated that the enzymes of cholera — Deneke, Miller, and Einkler — 
* Although the enzyme obtained from yeast can convert only the half of the 
cane sugar into dextrose, Payen has shown that the living yeast-cells convert 
the levulose also into dextrose, 
t Zeit. fiir Biol., Bd. v. 562. 
