Weiske[43] states that bone-gelatin, carefully freed from all mineral matter, is not precipitated by tannin till a trace of a salt (e. g. sodium chloride) is added. So far as is known, bone-gelatin is identical with that of skin. [43] Bied. Centr., 1883, p. 673. _Chondrin_ is the gelatinous body produced by the digestion of cartilage with water at 120° C. for three hours. In most of its physical properties it is identical with gelatin, but differs from the latter in being precipitated from its solution in water by acetic acid, lead acetate, alum, and the mineral acids when the latter are not present in excess. Chondrin also differs from gelatin in producing a substance capable of easily reducing cupric oxide when it is boiled for some time with dilute mineral acids. It is extremely probable that chondrin is merely an impure gelatine.[44] [44] Cp. Petri, Berichte, xii. p. 267; Mörner, Skand. Archiv f. Physiol., i. pp. 210-243; and Journ. Chem. Soc., 1889, A. p. 736 and Zeit. Physiol. Chem., 1895, xx. pp. 357-364; and Journ. Chem. Soc., 1895, A. i. p. 254. See also Richter, Org. Chem., i. p. 559. _Coriin._--Rollet[45] has shown that when hide and other forms of connective tissue are soaked in lime- or baryta-water, the fibres become split up into finer fibrils, and as the action proceeds, these again separate into still finer ones, till the ultimate fibrils are so fine as to be only distinguished under a powerful microscope. At the same time, the alkaline solution dissolves the substance which cemented the fibres together, and this may be recovered by neutralising the solution with acetic acid, when the substance is thrown down as a flocculent precipitate. This was considered by Rollet to be an albuminoid substance; but Reimer[46] has shown that it is much more closely allied to the gelatinous fibres, and, indeed, is probably produced from them by the action of the alkaline solution. Reimer used limed calf-skin for his experiments, and subjected it to prolonged cleansing with distilled water, so that all soluble parts must have been pretty thoroughly removed beforehand. He then digested it in closed glasses with lime-water for 7-8 days, and precipitated the clear solution with dilute acetic acid. He found that the same portion of hide might be used again and again, without becoming exhausted, which strongly supports the supposition that the substance is merely a product of a partial decomposition of the hide-fibre, and indeed that there is no distinct “cementing substance,” but merely a difference in the hydration or physical condition of the fibre substance which causes it to split more readily in certain directions. The dissolved substance, which he called “coriin,” was purified by repeated solution in lime-water and reprecipitation by acetic acid. It was readily soluble in alkaline solutions but not in dilute acids, though in some cases it became so swollen and finely divided as to appear almost as if dissolved. It was,