THE BLOOD. 251 



of the carbon monoxid with the hemoglobin. The compound thus formed 

 is very stable and resists the action of various reducing agents. The passage 

 of air or of some neutral gas through the blood for a long period of time will 

 gradually displace the carbon monoxid and enable the hemoglobin again to 

 absorb oxygen. It is for this reason that partial poisoning with the gas is 

 not fatal. It is to its power of displacing oxygen and forming a stable com- 

 pound with hemoglobin and thus interfering with its respiratory function 

 that carbon monoxid owes its poisonous properties. ExarAined spectro- 

 scopically, solutions of carbon monoxid hemoglobin exhibit two absorption 

 bands closely resembling in position and extent those of oxyhemoglobin ; but 

 careful examination shows that they are slightly nearer the violet end of the 

 spectrum and closer together. (See Fig. no.) A useful test for CO blood 

 is the addition of caustic soda, which produces a cinnabar red precipitate. 



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 in medicolegal 

 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. This 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 vasated into the tissues. In its chemic composition and in its reactions 

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

 characteristic play of colors on the addition of nitric acid. 



The Stroma. The stroma of 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, 



