112 



ESSENTIALS OF rilKMH'AL PHYSIOLOGY 



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

 puscles. It differs from most other proteins in containing the element 

 iron ; it is also readily crystallisable. 



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

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

 oxyhaemoglobin ; the other condition is the deoxygenated or reduced 

 haemoglobin (better called simply haemoglobin). This is found in tin- 

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

 blood which is returning to the heart after it" has supplied 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 diffi- 

 culty from other animals, such as man, 

 ape, and most of the common mam- 

 mals. 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 experi- 

 ment. 



3. On a larger scale the crystals 

 may be obtained by shaking the blood 

 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. 



In nearly all animals the crystals are rhombic prisms ; but in the 

 guinea-pig they are rhombic tetrahedra (four-sided pyramids) ; in the 

 squirrel, hexagonal plates ; and in the hamster, rhombohedra and 

 hexagonal plates. 



Fro. 30. Oxyha3rnoglobi.il crystals magni- 

 fied : 1, from human blood ; 2, from the 

 guinea-pig ; 3, squirrel ; 4, hamster. 



