THE BLOOD 89 



Oxygen is contained in combination with the haemoglobin to form 

 oxyhaemoglobin. The corpuscles also contain a certain amount of 

 carbonic acid (see Respieation, at the end of this lesson). 



The pigment of the red corpuscles. — The pigment is by far the 

 most abundant and important of the constituents of the red cor- 

 puscles. It is a substance which gives the reactions of a proteid, but 

 differs from most other proteids in containing the element iron ; it 

 is also readily crystalhsable. 



It exists in the blood in two conditions : in arterial blood it is 

 combined loosely with oxygen, is of a bright red colotu", and is called 

 oxyhaemoglobin ; the other condition is the deoxygenated or reduced 

 haemoglobin (better called simply haemoglobin). This is found in the 

 blood after asphyxia. It also occurs in all venous blood — that is, 

 blood which is returning to the heart after it has suppHed the tissues 

 with oxygen. Venous blood, however, always contains a considerable 

 quantity of oxyhaemoglobin also. Haemoglobin is the oxygen-carrier 

 of the body, and it may be called a respiratory pigment. 



Crystals of oxyhaemoglobin may be obtained with readiness from 

 the blood of such animals as the rat, 

 guinea-pig, or dog ; with difficulty 

 from other animals, such as man, ape, 

 and most of the common mammals. 

 The following methods are the best : — 



1. Mix a drop of defibrinated 

 blood of the rat on a slide with a 

 drop of water ; put on a cover glass ; 

 in a few minutes the corpuscles are 

 rendered colourless, and then the 

 oxyhaemoglobin crystallises out from 

 the solution so formed. 



2. Microscopical preparations may 

 also be made by Stein's method, which 

 consists in using Canada balsam in- 

 stead of water in the above experiment. 



3. On a larger scale the crystals pjc. 30.-Oiyhffiinogiobm crystals magni- 

 may be obtained by mixing the blood J^^ei^Srsf^^'r? L^«^ '"' 

 with one-sixteenth of its volume of 



ether ; the corpuscles dissolve and the blood assumes a laky appear- 

 ance. After a period, varying from a few minutes to days, abundant 

 crystals are deposited. 



The accompanying figures represent the form of the crystals so 

 obtained. 



