106 CHAPTER 10. 



204. The white corpuscles. 



The origin and functions of the white corpuscles are not clearly ascer- 

 tained. By some they are regarded as identical with lymph and chyle 

 cells, and it is thought that they become changed in the ductless glands 

 and absorbents into red cells or corpuscles. During inflammation they 

 are converted into pus cells, and it is also probable that they may become 

 converted into the cell elements of new tissues. By others the walls of 

 the white corpuscles after rupture are supposed to constitute the fibrin. 

 In many morbid states of the blood of an inflammatory character the 

 microscope shows the white cells to be in excess, and analysis shows that 

 the elements of fibrin are also in excess. They are supposed to be 

 generated either in the blood or in the lymphoid tissues of the body. 



205. Coagulation of Hood. 



The spontaneous coagulation of blood after being drawn is caused by 

 the continued power of contraction in the fibrin. It is not completed, 

 when it takes place at all, in less than from twenty to forty hours. The 

 cause of the contraction and solidification of the fibrin in the blood, 

 whether in or out of the body, is not yet positively ascertained. Objec- 

 tions may be made to every theory yet propounded on the subject. Dr. 

 Richardson's idea, that the coagulation is due to or at least attended by 

 loss or evolution of the ammonia contained in the blood was, until lately, 

 generally received; but is now much doubted. A small quantity of 

 ammonia added to blood, when drawn from the body, will certainly pre- 

 vent its coagulation ; whilst, on the other hand, a clot of blood will dis- 

 solve, if treated with ammonia. We only know, however, positively, 

 that rest, warmth, free access of air, and multiplication of the points of 

 contact favour coagulation. The withdrawal of the influence of the living 

 vessels is also in all probability largely instrumental in producing this 

 result. 



Whatever, however, may be the ultimate cause of coagulation in blood, 

 it is certainly affected by many and various circumstances, such as the 

 rapidity or otherwise with which the blood is drawn, and whether it is 

 taken from a large or small orifice, the temperature of the weather, the 

 amount of fibrin contained in it, the condition of the animal, the amount 

 of exercise he may have had immediately before being bled, the shape of 

 the vessel into which it is drawn, whether shallow, deep, or narrow, &c. 



The older Veterinarians attached much importance to the appearance 

 of the blood, to the presence or absence of a buffy coat, i. e. the absence 

 of red corpuscles from the upper clot, &c., as indicative of various diseases 

 or stages of disease ; but from the above it will be seen that the causes 

 which affect or modify its condition, are so numerous and varied, that 

 but little reliance can be placed on its appearance after it is drawn. 



206. Arterial and Venous blood. 



There are two kinds of blood in the body, namely, Arterial and Venous. 

 Arterial differs from venous blood in the following particulars : 1st, it is 



