A MANUAL OF 

 VETERINARY PHYSIOLOGY 



CHAPTER I 



THE BLOOD 



The special functions of the blood are to nourish all the tissues 

 of the body, and thus aid in their growth and repair ; to furnish 

 material for the purpose of the body secretions, to supply the 

 organism with oxygen, without which life is impossible, and finally 

 to convey from the tissues the products of their activity. To 

 enable all this to be carried out the blood is constantly in circula- 

 tion, is rapidly renewed, is instantaneously purified in the lungs, 

 and, by means of certain channels, is placed directly in com- 

 munication with the nourishing fluid absorbed from the intes- 

 tines, by which it is constantly repaired. 



Physical Characters. — Blood is a red, opaque, rather viscous 

 fluid, the tint of which depends upon whether it is drawn from 

 an artery or a vein ; in the former it is of a bright scarlet colour, 

 whilst in the latter it is of a purplish red. The colour is due to a 

 pigment called haemoglobin contained in the red corpuscles. 

 Whether the colour is scarlet, as in blood from an artery, or 

 purplish, as from a vein, depends on the difference in the amount 

 of oxygen with which the haemoglobin is combined. 



Owing to the reaction given by blood to ordinary test-papers, 

 the fluid has hitherto been described as alkaline in reaction. New 

 methods in physical chemistry * have, however, shown that blood 

 possesses little more alkalinity than distilled water, and may for 

 practical purposes be regarded as neutral. 



Sodium carbonate, which exists largely in blood and was 

 believed to confer alkalinity on this fluid, is now known to form 

 bicarbonate with the carbonic acid present, and this yields no 

 alkalinity on dissociation. The apparently alkaline reaction 



* The reaction of a solution is determined by the proportion of hydrogen 

 and hydroxyl ions. If hydrogen ions are in excess, the fluid is acid ; if 

 hydroxyl ions predominate, an alkaline reaction exists. 



