NITR O GENO US ME TAB OLISM IN THE TISS UES. 8 9 7 
lafcing proteid," while the proteid which is assumed to actually form the 
living substance of the tissues is termed hy Voit, Uiyancu'riss, which 
may be rendered in English by "organ- or tissue-proteid." l 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 Pfluger 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 Ernahrung," 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 
[Ztsehr.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 Tschiriew (Ber. d. k. sacks. Gesellsch. d. Wissensch., 1874, S. 411) and Forster [Sitewngsb. 
d. l-.-bcvier. AJcad. d. Wissensch. zu Miinchen, 1875, S. 206) seemed to show, transfusion 
of blood does not increase the proteid metabolism of the body. Pfliiger, however {he. cit., 
infra, pp. 362 et seq.) has shown that the results of Tschiriew aud Forster are capable of 
a diametrically opposite interpretation. 
2 Arch./, d. ges. Physiol., Bonn, 1893, Bd. liv. S. 333. 
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