252 TEXT-BOOK OF PHYSIOLOGY 



Carbo-hemoglobin. When hemoglobin is exposed to an atmosphere 

 of oxygen and carbon dioxid, it will absorb the latter as well as the former, 

 though the union of the oxygen under such circumstances is not as strong 

 as when oxygen alone is present. To the compound formed by the union of 

 the carbon dioxid and the hemoglobin the name carbo-hemoglobin has been 

 given. * The union, however, is not very stable as the carbon dioxid can be 

 readily dissociated. As the carbon dioxid absorption will take place, 

 even though the hemoglobin is practically saturated with oxygen, the as- 

 sumption has been made that the oxygen combines with hemochromogen, 

 and the carbon dioxid with the protein constituent globin. If this be the 

 case the hemoglobin and hence the red corpuscle, can be regarded as con- 

 cerned in the absorption and transmission of carbon dioxid from the tissue 

 to the lungs. 



Methemoglobin. This is a pigment, closely related to oxyhemoglobin, 

 found in the blood after the administration of various drugs, in cysts and in 

 the urine in hematuria and hemoglobinuria. It is also produced when a 

 solution of hemoglobin is exposed to the air and becomes acid in reaction 

 and brown in color. The spectrum shows two absorption bands similar to 

 oxyhemoglobin, but in addition a new and quite distinct band near the line 

 C, in the red. If the acid solution be rendered alkaline by the addition of 

 ammonia, this band disappears and another makes its appearance near the 

 line D. The addition of ammonium sulphid develops reduced hemoglobin, 

 which, on the absorption of oxygen, produces again oxyhemoglobin, as 

 shown by the spectroscope. 



Hematin. Boiling hemoglobin or adding to it acids or alkalies decom- 

 poses it and develops one or more protein bodies to which the general term 

 globulin has been given, and an iron-holding pigment termed hematin. 

 This is regarded as an oxidation product of hemoglobin and constitutes 

 about 4 per cent, of its composition. When obtained in a pure state, it is a 

 non-crystallizable blue-black powder with a metallic luster. According as 

 it is treated with acids or alkalies, two combinations of hematin can be 

 obtained (acid and alkaline), each of which has special properties, giving 

 rise to different absorption bands. 



Hemin. This pigment is a derivative of hematin, presenting itself in 

 the form of microscopic rhombic plates or rods (Teichmann's crystals), 

 which are so characteristic as to serve as tests for blood-stains inmedicolegal 

 inquiries. These crystals are readily obtained by adding to a small quantity 

 of dried blood on a glass slide a few drops of glacial acetic acid and a crystal 

 of sodium chlorid; after heating gently for a few minutes over a spirit lamp 

 and then allowing the mixture to cool, crystallization of the hemin soon takes 

 place. 



Hematoidin. The term has been applied to a pigment which occurs 

 in the form of yellow crystals in old blood-clots or in blood which has been 

 extra vasa ted into the tissues. In its chemic composition and in its reaction 

 it closely resembles bilirubin, the pigment of the bile, exhibiting the same 

 characteristic play of colors on the addition of nitric acid. 



The Stroma. Thestromaof the red corpuscles obtained by the methods 

 which dissolve out the hemoglobin has been shown by analysis to consist of 

 from 60 to 70 per cent, of water and 40 to 30 per cent, of solid material, 

 containing a proteid resembling cell-globulin, lecithin, cholesterin, and 

 norganic salts, among which potassium phosphate is especially abundant. 



