898 METABOLISM. 



Voit 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, 2 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 Giirber, and of Schondorflf (with Pfliiger), which will be subse- 

 quently referred to. 



The arguments and experiments by which Voit 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 Voit 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. tit., S. 303. 



2 " Ich will also nicht damit einen chemischen Unterschied bezeicbnen, sondern 

 zunachst nur einen Unterschied in dem Orte an dem es sich befindet. . . . Ein und dasselbe 

 Molekiil Eiweiss kann in einem bestimmten Momente Eiweiss des Blutplasmas, in einem 

 nachsten Eiweiss der Ernabrungsflussigkeit, in einem anderen Eiweiss der Lymphe oder 

 auch Organeiweiss sein " (loc. cit., S. 301). 



3 Loc. tit. 



