NITROGENOUS METABOLISM IN THE TISSUES. 897 



lating proteid," while the proteid which is assumed to actually form the 

 living substance of the tissues is termed by Voit, Organeiweiss, which 

 may be rendered in English by "organ- or tissue-proteid." 1 If the 

 term " circulating proteid " be used to include the proteids of the blood 

 and lymph as well as those which occur in the actual interstices, if 

 any, of the bioplasm, no exception can be taken to it, but if it 

 is used, as has been sometimes done by Voit, in a restricted sense, 

 merely to indicate proteid material which is interpolated amongst the 

 molecules of the proteid forming the bioplasm, without itself actually con- 

 stituting part of that substance, it must be admitted with Pfliiger 2 that 

 such employment of the term can only be misleading. Using, however, 

 the term circulating or unorganised proteid in the wider sense, there are 

 still two possibilities open as to the manner in which the proteids of the 

 body undergo metabolic changes (1) We may assume that the circu- 

 lating proteid, reaching the tissues and becoming imbibed by them, 

 must be completely incorporated and built up into them before it is 

 split up and oxidised ; or (2) it is open to us to suppose that the 

 unorganised proteid may be split up and oxidised outside the actual 

 molecules of the organised proteid of the living substance, but as a 

 consequence of the action of that substance. In the one case we may 

 suppose it to produce a direct formation or building up of bioplasm a 

 transformation, in fact, of unorganised into organised proteid ; in the 

 other case, as undergoing contact changes by the action of the bioplasm, 

 much in the same way as contact changes are brought about by organised 

 ferments. 



One reason for believing that the circulating proteid only becomes 

 in part built up into the material of the bioplasm, is derived from the 

 following observation (Voit). If, to an animal kept upon a diet con- 

 sisting of non-proteid food (fat), gelatin is given in an amount sufficient 

 to replace a caloric equivalent of such non-proteid material, it is found 

 that, reckoning for the amount of nitrogen due to the metabolised 

 gelatin, which always appears in full as urea, there is less nitrogen given 

 off from the body than before ; that is to say, there is less tissue substance 

 broken down. But in the total absence of nitrogenous food there is a 

 definite amount of body proteid metabolised ; and since, when gelatin 

 is given, it is metabolised instead of part of this proteid, although it 

 cannot itself be built up into tissue substance (p. 878), it must be 

 assumed that the gelatin has taken the place of proteid which, although 

 in such intimate contact with the bioplasm as to become metabolised 

 under its influence, did not actually form bioplasm. It may further 

 be argued that the rapidity with which metabolic changes in proteids 

 occur within the body, and the large amount of such metabolism, when 

 excess of proteid is taken as food, render it improbable that all meta- 

 morphosed proteid has been built up to form bioplasm. 



1 C. Voit, "Die Ernahrang," Hermann's "Handbuch," Bd. vi. S. 301. The terms 

 "organised" and "unorganised" proteid are preferable to "tissue-" and "circulating-" 

 proteid, which have been used at different times in different senses. In earlier publications 

 (Ztsclir. f. BioL, Miinchen, 1874, Bd. x.) Voit included the proteids of blood plasma under 

 the designation "Organeiweiss," founding this view upon the fact that, as the experiments 

 of Tschirievv (Ber. d. k. sdchs. Gesellsch. d. PTissensch., 1874, S. 411) and Forster (Sitzungsb. 

 d. k.-bayer. Akad. d. Wisscnsch. zu Miinchen, 1875, S. 206) seemed to sho\v, transfusion 

 of blood does not increase the proteid metabolism of the body. Pfliiger, however (loc. cit., 

 infra, pp. 362 et seq.) has shown that the results of Tschiriew and Forster are capable of 

 a diametrically opposite interpretation. 



2 Arch.f. d. ges. Physiol., Bonn, 1893, Bd. liv. S. 333. 



VOL. i. 57 



