CREATINE, or KnE'iorixli (Gr. lavas, flesh), was discovered in 18.3 by Chevreul, but little was known about it till Liebig published his Researches on the Ultenti.dry of Irbod, in 1847. From his investigations, and those of subsequent chemists—amongst whom we may especially name the late Dr. William Gregory, of Edinburgh—the fol lowing facts regarding its properties and occurrence have been established.
C. forms transparent, glistening crystals, belonging to the clinorhombic system, and usually occurring in groups, the character of which is exactly similar to that of sugar of lead. Although usually grouped among the basic bodies, it is neutral in its reac tion. It dissolves in 74.4 parts of cold water, and in boiling water in such quantity that the solution on cooling solidifies into a mass of delicate needles. These crys tals contain two atoms of water and one atom of anhydrous C., whose compositiou. according to Liebig, is represented by the formula There is no direct chemical test for the detection of C., and the methods which have been employed to obtain it are too complicated for insertion in this article.
C. is constantly present in the juice both of voluntary and involuntary muscles. The quantity differs in the flesh of different kinds of animals, and even in different muscles of the same animal, but is always very small; and lean animals yield relatively more than fat ones. According to Liebig, the flesh of hens yields the largest amount, viz., 0.82 per cent, the average quantity from horse or ox flesh being 0.07 per cent. Gregory determined its amount in the flesh of various mammals, birds, and fishes; and Schlossherger found 0.067 per cent in human flesh. It has likewise been detected in very- small quantity in the blood of oxen, also in the liquor amnii of women who have died in advanced pregnancy, and it can usually be obtained from the urine, although it is doubtful whether it is a normal constituent of that fluid. It does not exist in the liver or kidneys, but has been found among the soluble constituents of the brain.
Although the view has been advocated that, from its occurrence in flesh, and from its large amount of nitrogen (32.06 per cent), it must be an important nutritive agent, there are most decisive reasons for opposing this opinion, and for ranking it among the products of excretion; for, in the first place, if it could be employed with further advantage in the organism, it (or its near ally, creatinine) would not be allowed to escape by the kidneys; secondly, the readiness with which it may be converted into unques tionable products of excretion (as, for instance, into urea, by the action of heat and baryta water), proves its approximation more nearly to these substances, than to such bodies as albumen or fibrin; and thirdly, there is no instance of a tissue-forming food occurring in a crystalline form.
ClIkATININE is closely allied in its chemical and physiological relations to creatine. Liebig found that, when heated with a strong mineral acid, a solution of creatine no longer yields crystals of that substance, but a new body of totally different chemical properties, to which he gave the name of creatinine. Its chemical composition is rep resented by the formula and on comparing this formula with that for crea tine, we see that the conversion of the latter into the former, by the action of mineral acids, depends upon the separation of the elements of water. Liebig shortly after wards detected C. as a constituent of the muscular juice. In the latter fluid, it occurs in less quantity than creatine; while in the urine, where it is also found, it is the abundant of the two. Traces of it have also been found in the blood and in the liquor amnii.
C. crystallizes in oblique rhombic prisms, is a most decided alkaloid, reacting strongly on vegetable colors, and having almost as caustic a taste as ammonia; it further differs from creatine in its far greater solubility in water, alcohol, and ether. There can be little doubt that C. takes its origin from creatine.