898 METABOLISM. 
Yoit has drawn a much sharper distinction between the organised and 
unorganised (tissue and circulating) proteid than that above indicated. He 
denies that tissue proteid can as such undergo metabolism, even in inanition. 
According to his view, it must first be dissolved up and take the form of 
circulating proteid, and be carried in this form to other tissues {e.g. from the 
muscles to the heart and nervous system), to be metabolised as circulating 
proteid in these. 1 This view is, however, difficult to reconcile with the 
supposition that there is no chemical difference between the two forms of 
proteid,- for if there is no such difference, it is not clear why the proteid 
should not become metabolised in the tissues themselves, but should need to 
be conveyed outside them before undergoing metabolic changes. Moreover, it 
is entirely inconsistent with the experiments of Oertmann and Pfliiger, of 
Pembrey and Gurber, and of Schondorff (with Pfliiger), which will be subse- 
quently referred to. 
The arguments and experiments by which Yoit has endeavoured to support 
his position are, however, quite insufficient to carry conviction, and it must be 
regarded as having been rendered completely untenable by the experiments 
and criticisms of Pfliiger. 3 A view exactly the contrary to that of Yoit was 
taken by Liebig, and has been maintained by Hoppe-Seyler, and in a some- 
what qualified form by Pfliiger. According to this view, it is only organised 
proteid which can undergo metabolic changes — never unorganised. Unorgan- 
ised proteid must therefore first be converted into organised before it is 
capable of metabolism ; in other words, tissue bioplasm must be built up out of 
circulating proteids before these last, which then of course have become 
tissue proteids, can be broken down and oxidised. It is therefore denied that 
any metabolism of proteids can occur outside the actual molecules of the living 
substance — that, in short, there can be any contact action. It has, however, 
been shown in the case of yeast, that chemical action may take place outside 
the living cells, although under their direct agency, so that the possibility of 
metabolic changes occurring under the influence of, but outside, the actual 
molecules of the protoplasm of cells cannot be denied. Moreover, it is not 
probable that the non-proteid materials (fat, carbohydrate, gelatin) of the 
food become after assimilation built up into bioplasm, and although they are 
undoubtedly taken into cell protoplasm they can hardly be regarded as 
forming constituent parts of the molecules of its bioplasm. In this sense, 
therefore, they are outside, although in contact with, the bioplasm of the 
tissues.; nevertheless they are found to undergo metabolic changes under the 
influence of that substance. It may, of course, be argued that they also are 
really built up into the living proteid molecule, and must be so before they 
can become metabolised, but there is absolutely no evidence that this is the 
case, or that fat or carbohydrate are necessary constituents of bioplasm. 
The fat drops which we see embedded in the protoplasm of cells, are 
certainly not constituent parts of the bioplasm, although under its influence 
they undergo physical and chemical changes, and the same is the case with 
the glycogen clumps which can be seen in the liver cells, to say nothing of 
the starch, aleuron, and fat granules of vegetable cells. The phenomenon of 
contact change is in short too universal to be denied. Since this is so, the 
most reasonable view to be taken of the matter appears to be one which 
supposes that metabolism may occur both as a splitting-up and oxidation of 
the molecules of living tissue or bioplasm, and as a splitting-up and oxidation 
1 Loc. cit., S. 303. 
2 " Ich will also nicht damit einen chemiscken Unterschied bezeichnen, sondern 
zunaehst nur einen Unterschied in dem Orte an deru es sieh befindet. . . . Ein und dasselbe 
Molekiil Eiweiss kann in einem bestimniten Moruente Eiweiss des Blutplasmas, in einem 
nachsten Eiweiss der Ernahrungsflussigkeit, in einem anderen Eiweiss der Lymphe oder 
auch Organeiweiss sein " (loc. cit., S. 301). 
3 Loc. cit. 
