88o METABOLISM. 



The phosphorus of any nuclein 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 Miescher, 1 who found 

 in the case of the salmon, which travels from the sea to the upper 

 Khine, 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 0*2 per cent. 

 Injected too rapidly, or in too large doses (more than 1 grm. per kilo, 

 body weight), glycosuria results ; 5 and if its elimination by the kidneys 



1 Arch.f.Anat. u. Entivcklngsgecch. , Leipzig, 1881, S. 193 ; and "Statistische u. biol. Beitr. 

 z. Kenntniss vom Leben des Rheinlachses," 1880 (quoted from Bunge's " Handbtich "). 



2 Weiske, Ztschr. f. Biol., Munchen, 1879, Bd. xv. S. 261 ; 1881, Bd. xvii. S. 415 ; 

 1884, Bd. xx. S. 277 ; 1894, Bd. xxx. S. 254 ; Zuntz and Bahlmann, Arch. /. 

 Physiol., Leipzig, 1882, S. 424 (Verhandl. d. phys. Gesellsch.) ; Potthast, Arch. f. d. yes. 

 Physiol., Bonn, 1883, Bd. xxxii. S. 280 ; I. M.mik,'Virchow's Archiv, 1883, Bd. xciv. S. 436 ; 

 and 1884, Bd, xcviii. S. 364 ; Mauthner, Ztschr. f. Biol., Miinchen, 1892, Bd. xxviii. 

 S. 507 ; E. Voit, Sitzunysb. d. k.-bayer. Akad. d. Wissensch. zu Munchen, 1883, S. 401 ; 

 Ztschr. f. Biol., Munchen, 1892, Bd. xxvii. S. 492; 1893, Bd. xxix. S. 125; Gabriel, ibid., 

 S. 115. 



3 Meissner, Ztschr. f. rat. Med., 1868. Bd. xxxi. S. 283. 



4 According to Dastre (Arch, de physiol. norm, etpath., Paris, 1889, p. 718), galactose is 

 directly assimilable. 



5 Biedl and Kraus ( Wien. klin. Wchnschr., 1896, S. 55) state, however, that they were 

 able to inject as much as 200 to 300 grms. 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. 



