HEMOGLOBIN, an organic coloring mat ter, which constitutes about nine-tenths of the weight of dried red blood corpuscles, and serves as a carrier of oxygen from the lungs to the general tissues of the body. It is an ex ceedingly complex substance, and its formula is not certainly known. It is a chromoprotein and has an interesting history. Iron is found throughout nature and early became incorporate within living matter as an energy transformer. In order to transform energy, oxygen chiefly and yet not by itself, oxidizes and is thus de stroyed, a peculiar substance being formed which in plants seems to develop with the pro teid of chlorophyll and in animals into What is called hemoglobin. In the lowest worms and mollusks this iron compound is known. In these low forms it is found as a part of the muscle substance itself. When the blood scheme arose in higher animals it then entered into that fluid as an oxygen carrier. The complex uses to which it Is put lie outside of this article. Zinoffsky gives it as CinflanNu4S2FeOus; but this can hardly be regarded as more than a guess. According to many authorities, hemoglo bin is not a definite chemical compound, but a more or less variable mixture of simple sub stances. It gives all the general reactions of the proteids, but, unlike most of the proteids, it may easily be obtained in crystalline form, its crystals commonly occurring in rhombic plates or prisms, varying somewhat in shape, according to the source from which the substance is pre pared. The exceeding physiological importance of hemoglobin depends upon the fact that it readily combines with oxygen to form a very unstable compound known as oxyhemoglobin. The combination takes place as the blood corpuscles containing the hemoglobin pass through the lungs; and the loosely-combined oxygen is given off again as the corpuscles pass through the capillaries, the oxyhemoglobin being thereby again reduced to hemoglobin. Hemo globin also combines with carbon monoxide to form a similar but far more stable substance known as carboxyhemoglobin. In poisoning by the inhalation of coal-gas the carbon monoxide present in the coal-gas combines with the hemo globin in the lungs, and the carboxyhemoglobin so formed does not break up again. As the
absorption of the coal-gas proceeds, a continu ally increasing quantity of hemoglobin is there fore destroyed, so far as its utility as an oxygen carrier is concerned. In extreme cases of such poisoning, transfusion of blood is resorted to, in order that the patient may have a sufficient supply of hemoglobin to transport the requisite quantity of oxygen from the lungs to the other tissues of the body.
Crystals of hemoglobin have been prepared. Pure hemoglobin has a purplish color, which gradually passes into a scarlet or a yellowish red, as the substance absorbs oxygen and be comes thereby converted into oxyhemoglobin. Carboxyhemoglobin is even more brilliantly red than oxyhemoglobin: All three of these sub stances exhibit marked absorption spectra when in solution, and very small quantities of them can be easily detected by the spectroscope. It is said that the presence of one part of hemo globin in 10,000 parts of water can be distinctly demonstrated by this means.
When oxyhemoglobin is acted upon by acids or alkalis, or by the gastric juice, it is resolved into a proteid substance and a definite com pound which has the probable formula CesHi.Ns P'e,Oie and is known as hematin. Hematin may be best prepared by extracting blood clot, directly, with hot alcohol to which a small quan tity of sulphuric acid has been added. The ex tract is next agitated with chloroform, which takes up the hematin. The chloroform is .then separated, washed with water to remove the acid, and allowed to evaporate, when the hem atin is deposited in the form of a bluish-black powder. Hematin is a very stable compound, and may be heated to F. without decom position. At higher tempeiatures it burns with evolution of hydrocyanic acid, leaving an ash composed chiefly of oxide of iron. It is in soluble in water, ether, dilute acids' and pure alcohol; but it dissolves readily in solutions of the caustic alkalies, and in alcohol to which a small quantity of sulphuric acid has been added. Consult Stirling, 'Physiology); Bayliss, 'General Physiology); Matthews, 'Physiological Chemistry.)