30 A Manual of Veterinary Physiology. 



it obtains at the lungs, and leaves behind it in the tissues. 

 The hemoglobin of the red cells, therefore, exists in two 

 states, one in which it is charged with oxygen, called oxy- 

 hemoglobin, and the other in which it has lost its dxygen, 

 known as reduced hemoglobin. The process of oxidation 

 and partial reduction is constantly occurring at every revo- 

 lution of the circulation, with the ultimate result that the 

 red blood disc gets worn out and dies. In this condition it 

 is cast off from the system, being got rid of through the 

 medium of the liver as bilirubin, and also, probably, being 

 destroyed in the spleen and elsewhere. When the red cells 

 die their hemoglobin is set free, and is decomposed into 

 hseinatin, from which, probably, all the pigments of the 

 body, but especially those of the bile, are formed. 



The probable origin of the red cells is in the red marrow 

 of bones ; all other seats of formation appear doubtful. It 

 is certain that their production is a matter of extreme 

 rapidity, as may be witnessed, for example, after haemor- 

 rhage. The red cells are not derived from the white. In 

 the embryo the red cells are nucleated during the early 

 period of development, but are gradually replaced by non- 

 nucleated corpuscles before birth. 



In speaking of the plasma, we mentioned the con- 

 tradictory results obtained by various observers as to the 

 proportion the plasma bore to the cells. According to 

 some authorities, the blood cells are 35 to 40 per cent, of the 

 weight of the blood. M'Kendrick gives the proportion of 

 red cells as 33 per cent., or -*- ; whilst Bunge, from an 

 analysis of horse's blood, puts the red cells at 53 per cent., 

 and the plasma at 47 per cent. It is probable that all these 

 results were true for the specimen of blood examined, for 

 there can be no doubt of the variation in the composition 

 of this fluid. 



We have mentioned that retained in the pores of the 

 stroma of the red cells is the red colouring substance 

 haemoglobin, and with this we must now deal. 



Haemoglobin, also known as hsemato-globulin, and 

 hemato-crystalline, is a most remarkable body ; it is a 



