HIE'IVIOGLOIBIN (from Gk. alpa, haima, blood + Lat. plobus, ball). An important sub stance found in red blood-corpuscles, and hav ing the property of readily taking up oxygen from the air, and just as readily giving it up to the tissues of the body. The chemical na ture of haemoglobin is as yet little understood, and even its true chemical composition is un known. The compound of haemoglobin with oxy gen, called oxy-humoglobin, may be converted into haemoglobin by keeping its concentrated aqueous solution for some time in a sealed tube. Crystal line haemoglobin has a dark-red color, which dif fers somewhat with the direction from which the crystals are viewed. The crystals are very soluble in water, and combine readily not only with oxy gen, but also with nitric oxide, carbon monoxide, and probably with carbon dioxide. When treated with acids or alkalies, haemoglobin is decomposed, yielding (1) a proteid called globin, and (2) a colored substance known as reduced hxmatin, or lixmochronagen, which is readily converted, by oxidation, into hamatin (q.v.).
Oxy-hamoglobin, and probably haemoglobin it self, vary in chemical composition and in certain physical properties according to the source from which they are obtained. The preparation of a considerable quantity of oxy-hwinoglobin from the blood of certain animals is a matter of some difficulty. To obtain oxy-humoglobin from dog's
blood, the latter is defibrinated, strained, shaken with ether, and cooled, the oxy--hiemoglobin sepa rating out in the form of a crystalline mass; it may be purified by recrystallizing from very lit tle cold water, a small amount of alcohol being added to the aqueous solution. The crystals of oxy-hxmoglobin have a bright scarlet color like that of arterial blood. Their constituent elements are carbon, hydrogen, oxygen, nitrogen, sulphur, and iron. Nothing, however, is known of the chemical structure of oxy-haemoglobin, and its molecular weight appears to be at least as high as 13,000.
Carbon-monoxide hemoglobin may be obtained by passing carbon-monoxide gas through an aqueous solution of oxy-humoglobin. The highly poisonous action of carbon monoxide is due to the formation of this stable compound in the blood, by which the latter loses its capacity for carrying oxygen. Caustic soda solution pro duces, in blood containing carbon-monoxide }he moglobin, a brilliant red precipitate; in normal blood the precipitate is brownish-green; the pres ence of carbon monoxide in blood may thus be readily demonstrated.