880 METABOLISM. 
The phosphorus of any rmclein which is absorbed is probably converted 
into phosphoric acid, and excreted as phosphates by the urine. There 
is no evidence that the nuclein which is absorbed is taken up by the 
tissues, and by them again converted into tissue nucleins ; it is more 
probable that these arise by independent synthesis from proteid and 
phosphates. That this may occur was shown by Mieseher, 1 who found 
in the case of the salmon, which travels from the sea to the upper 
Ehine, there to deposit its spawn, and which during the whole period of 
its journey and sojourn in the river, lasting some weeks or even months, 
takes no food whatever (the alimentary canal being always found empty), 
that the ovaries increase in size at the expense of the muscular tissue. 
Now the ovaries, being mainly composed of ova, contain large quantities 
of nuclein and lecithin, whereas the muscles contain mainly ordinary 
proteids and very little of these substances ; the latter must therefore 
be formed by synthesis, the materials for such synthesis being derived 
from the proteids, the fats, and the phosphates of the muscles. 
Amido - acids. — Experiments to determine the nutrition, and 
especially the proteid-sparing value of amido-acids, have chiefly been 
made with asparagin, which occurs in some quantity in certain vegetables. 
The general result of these inquiries is to show that in herbivora (rabbit, 
goose, sheep), the amido-acids can act as proteid-sparers, whereas in 
carnivora (dog) and omnivora (rat) they have not proteid-sparing 
effects when added to the diet. 2 
Creatine has been found to have no nutritive value. If given with 
the food, it appears wholly in the urine as creatinine. 3 
Carbohydrates. — Apart from the small amount of glycogen or sugar 
which may be contained in flesh foods, and from the lactose of milk, the 
carbohydrates of the food are wholly derived from the vegetable king- 
dom. The chief carbohydrate constituents of an ordinary diet are starch 
and cane-sugar, with a certain amount of grape-sugar when there is 
much consumption of certain fruits. Neither starch (in solution) nor 
cane-sugar (Bernard) is directly assimilable when injected into the blood 
vessels, and the same is true for maltose and lactose. 4 These sub- 
stances all appear under such circumstances at once in the urine. 
On the other hand, dextrose can be directly assimilated, even in large 
amounts. It is necessary that the injection should be conducted slowly, 
so that the liver should have time to convert it into glycogen before the 
proportion of dextrose in the blood much exceeds about 02 per cent. 
Injected too rapidly, or in too large doses (more than 1 grin, per kilo, 
body weight), glycosuria results ; 5 and if its elimination by the kidneys 
1 Arch.f.Anat. u.Entuxklngsgccch., Leipzig, 1881, S. 193 ; and "Statistische u. biol. Beitr. 
z Kenntniss vom Leben des Rheinlachses," 1880 (quoted from Bunge's "Handbuch"). 
- Weiske, Ztschr. f. Biol., Miinchen, 1879, Bd. xv. S. 261 ; 1881, Bd. xvii. S. 415 ; 
1884, Bd. xx. S. 277 ; 1894, Bd. xxx. S. 254 ; Zuntz and Bahlraann, Arch. f. 
Physiol., Leipzig, 1882, S. 424 ( VerhaiuM. d. phys. Gescllsch.) ; Potthast, Arch.f. d. gcs. 
Physiol., Bonn, 1S83, Bd. xxxii. S. 2S0 ; I. Muuk, Vvrchow's Archw, 1883, Bd. xciv. S. 436 ; 
and 1884, Bd. xcviii. S. 364 ; Mauthner, Ztschr. f. Biol., Miinchen, 1S92, Bd. xxviii. 
S 507 ; E. Voit, Sitzimgsb. d. k. -layer. Akad. d. JVissensch. zu Miinchen, 1883, S. 401 ; 
Ztschr. f. Biol., Miinchen, 1892, Bd. xxvii. S. 492; 1893, Bd. xxix. S. 125; Gabriel, ibid., 
S. 115. 
3 Meissner, Ztschr. f. rot. Med., 1868, Bd. xxxi. S. 283. 
4 According to Dastre (Arch, dephysiol. norm, etpath., Paris, 1889, p. 71S), galactose is 
directly assimilable. 
5 Biedl and Kraus ( Wien. klin. Wchnschr., 1S96, S. 55) state, however, that they were 
able to inject as much as 200 to 300 gnus, of grape-sugar, in 10 per cent, solution, into the 
vein of a man, without producing either polyuria nor any but a slight temporary glycosuria. 
