The elements of the science of nutrition / by Graham Lusk.

  • Graham Lusk
Date:
1917
Catalogue details

Licence: In copyright

Credit: The elements of the science of nutrition / by Graham Lusk. Source: Wellcome Collection.

    80/850 (page 80)
    and “organized protein,” the more resistant living protein of the tissues themselves. Voit1 stated that in metabolism the lifeless pro- tein furnished to the cells by the blood was used in preference to the living organized tissue protein. He quoted Landois’ experiments, which show that after producing an artificial plethora through injec- tion of blood, the serum proteins are readily burned and their nitrogen eliminated in the urine, while the red blood-cells containing the organized protein are only slowly destroyed. If serum alone be transfused, its protein is rapidly destroyed2 (see p. 194). Even in starvation there is evidence of “circulating protein” as food for the tissues. Thus Miescher showed that the salmon, after entering the Rhine from the sea, virtually starves. Yet the genital organs of both male and female develop greatly, this being at the expense of the muscles, which may lose 55 per cent, of their weight. This protein must have been carried to the various parts of the body in the circulating blood-stream. Miescher finds no indi- cation of any destruction of muscle-fibers in this process of emaciation (see p. 310). It is interesting in this connection to note that A. R. Mandel3 has been able at a pressure of 300 to 350 atmospheres acting on lean meat seventy-two hours old to press out a fluid containing 44 per cent, of the protein present in the fibers, and this without visible change from the normal histologic appearance of the muscle. THE COMPOSITION OF PROTEIN It seemed quite possible that in ordinary starvation protein from muscle and other tissues passed to the blood and was carried to all the organs as circulating protein for the nutrition of their cells. The great work of Kossel, Hofmeister, and Emil Fischer has taught that the essential composition of protein is a structure formed of chains of amino-acids. It was Kossel4 who forecast the polypeptid nature of the protein molecule. Hofmeister,5 in a celebrated address at Carlsbad in 1902, marshalled the small amount of evidence then available and convincingly demonstrated that the union of amino- acids was the essential structural factor in the protein molecule. At 1 Voit, C.: L. Hermann’s “Physiologie,” Leipzig, 1881, 6, Pt. 1, p. 300. 2 Forster, J.: Z. f. Biol., 1875, 11, 496* 3 Mandel, A. R.: Unpublished work from the Munich Clinic of Prof. Fr. Muller. 4 Kossel, A.: Z. physiol. Chem., 1898, 25, 174; Ber. d. D. chem. Ges., 1901, 34, 3214. 5 Hofmeister, F.: Verhandl. d. Naturforscherversam., Carlsbad, 1902, p. 621; Ergeb. d. Physiol., 1902, 1, 795.