136 PRINCIPLES OP VETERINARY SCIENCE 



(Fig. 44) . They are surprisingly uniform in size, but are smaller 

 in mammals than in reptiles and amphibians. They originate 

 in the red marrow of bones and are destroyed in the liver and 

 spleen. In very thin layers they appear yellow in color, but 

 under ordinary conditions are red from the hemoglobin, a pig- 

 ment, which they contain. They give the blood its characteristic 

 red color. There are from 5 to 6 millions in each cubic millimeter 

 of blood. Calculations have placed the total surface of the red 

 corpuscles as high as one acre for one horse. 



Hemoglobin is a protein substance, making up about 90 per 

 cent, of the solid part of the erythrocytes. It has the remarkable 

 property of combining with oxygen in the lungs and of releasing 

 this gas when it comes into a situation where there is a relative 

 lack of the element, as is found in the tissues. The union in 

 the lungs of the hemoglobin and oxygen forms a temporary 

 chemical compound called oxyhemoglobin which is bright red 

 in color. As the blood flows through active tissues whose cells 

 crave oxygen the red corpuscles yield more or less of their oxygen. 

 Insofar as they do this, their oxyhemoglobin is changed to 

 what is known as reduced hemoglobin which is blue-black in 

 color and the more of it there is present the darker the blood. 



Blood-plates are bodies of smaller size than the red corpus- 

 cles. They are found in the blood. From the fact that they 

 disappear as soon as blood is drawn from the vessels, they are 

 thought to have something to do with the clotting of blood. 



Blood-plasma is the fluid part of living blood in which the 

 blood corpuscles live and are transported. It constitutes about 

 one-half the volume of the blood. Four-fifths of its total solids 

 are albuminous in character, consisting largely of fibrinogen, 

 nucleoprotein, serum-albumen, and serum-globulin. The signifi- 

 cance of these substances is obscure; at present they are thought 

 to be rather permanent, little subject to depletion, and not con- 

 sumed as food by the tissues. 



Blood-serum is the clear, amber-yellow fluid that is .expressed 

 from the clot when it shrinks. It differs from the plasma in 

 containing no fibrinogen. 



Blood clots or coagulates when it is taken from the blood-ves- 

 sels and after death. The property of clotting completely 

 checks hemorrhage from small vessels. A clot resembles jelly 

 and contains the same elements that are found in living blood 



Digitized by Microsoft® 



