The Chemistry of Cookery

[2] Tarchnoff has recently discovered the curious fact that the white of the eggs of birds that are hatched without feathers remains transparent when coagulated, while the eggs which produce chickens and other birds already fledged become opaque when coagulated. This is familiarly illustrated by the difference between plovers’ eggs and hens’ eggs when cooked. [3] ‘Egg-cement,’ made by thickening white of egg with finely-powdered quicklime, has long been used for mending alabaster, marble, &c. For joining fragments of fossils and mineralogical specimens, it will be found very useful. White of egg alone may be used, if carefully heated afterwards. [4] _Physiological Chemistry_, vol. ii. p. 356. [5] It was given to me in 1868. I have just found that some of it remains unused (December 1884), and that it still retains its characteristic flavour. CHAPTER IV. GELATIN, FIBRIN, AND THE JUICES OF MEAT. GELATIN is a very important element of animal food; it is, in fact, the main constituent of the animal tissues, the walls of the cells of which animals are built up being composed of gelatin. I will not here discuss the question of whether Haller’s remark, ‘Dimidium corporis humani gluten est’ (‘half of the human body is gelatin’), should or should not now, as Lehmann says, ‘be modified to the assertion that half of the solid parts of the animal body _are convertible, by boiling with water_, into gelatin.’ Lehmann and others give the name of ‘glutin’ to the component of the animal tissue as it exists there, and gelatin to it when acted upon by boiling water. Others indicate this difference by naming the first ‘gelatin,’ and the second ‘gelatine.’ The difference upon which these distinctions are based is directly connected with my present subject, as it is just the difference between the raw and the cooked material, which, as we shall presently see, consists mainly in solubility. Even the original or raw gelatin varies materially in this respect. There is a decidedly practical difference between the solubility of the cell-walls of a young chicken and those of an old hen. The pleasant fiction which