Secondly,--Two peculiar substances, named respectively, glycocholic, and taurocholic acid--the former yielding, when in combination with soda, a crystallizable, the latter a non-crystallizable salt. Taurocholic differs still further from glycocholic acid, in containing a large percentage of sulphur, {9} and being, under the influence of hydrochloric acid, convertible into taurine, a beautiful white crystalline substance. [Illustration: FIG. 2. Taurocholate of soda is found in the form of fatty-looking globules of various sizes. They differ from fat and oil globules, however, in being soluble in water, and insoluble in alcohol and ether.] Thirdly,--Cholesterine, a crystalline, fatty matter, not, however, peculiar to bile, but found in various tissues, and secretions of the body. [Illustration: FIG. 3. Cholesterine crystals appear in the form of fine transparent four-sided plates of various sizes and shapes. The crystals are freely soluble in hot alcohol, from which they are re-deposited on cooling.] {10} Fourthly,--A brown resinous substance resembling, in appearance and consistence, shoemaker's wax. Fifthly,--Among the constituents of the bile, I may mention sugar, for both in the normal bile of man, and of the lower animals, the ox, and the dog, I have detected that substance. On one occasion, I even found torulæ in the bile twenty-four hours after its removal from the gall-bladder of a healthy dog. Sixthly, and lastly,--a quantity of inorganic matter, consisting chiefly of soda, potash, and iron. The specific gravity of bile fluctuates, of course, with the percentage of solid matter it contains. From my own observations, I consider that healthy human bile has an average specific gravity of 1020, and contains about six per cent. of solid matter, five per cent. of which is organic, and one per cent. inorganic substance. When fresh, bile is almost neutral; but it rapidly undergoes decomposition, and becomes alkaline. In colour, human bile is usually of a brownish yellow hue; the colour, however, varies with its degree of concentration, the kind of food taken, and the state of the system. As regards the effect of food, if we may be allowed to form an opinion from experiments on dogs, it may be said that, as a {11} rule, animal food tends to give bile a yellow, vegetable food a green, tint. Next, as regards the manner in which bile is secreted. For a long time it was thought, and, indeed, some people still think, that bile exists pre-formed in the blood, and that the liver only excretes it, as the kidneys excrete the urinary ingredients. Another class, running to the opposite extreme, believe that the liver is not merely the excretive, but also the formative organ of the bile. It appears to me, however, that neither of these extreme views is correct, and that the truth lies between the two.