40k DADDS VETERINARY MEDICINE AND SURGERY. 



then, venous blood enters the pulmonary tissues. The arteriali- 

 zacion of the blood which follows is a process more essential to 

 vital integrity than the assimilation of food; for animals can live 

 a long time without food, but they can only exist a short time 

 unless the blood be oxygenized. 



The pulmonary arteries branch off into minute ramifications on 

 the surface of the air-cells of the lungs, and where these minute 

 divisions terminate others commence, termed venous radicles, 

 which ultimately become large veins. By the pulmonary veins 

 the oxygenized blood is returned to the left auricle and ventricle 

 of the heart. This route of the blood from heart to lungs, and back 

 again from lungs to heart, is termed the lesser circulation. The 

 left ventricle delivers the blood into the great aorta, and thence 

 to every part of the body. This is called the greater circulation. 



Difference between Veins and Arteries. — The veins differ from 

 arteries in being less dense, having no muscular nor ligamentary 

 tunics like the arteries, and, therefore, offer but little resistance to 

 tight collars and tight-fitting harness and circingles, which are apt 

 to interfere with the return of blood to the heart. The incapacity 

 of veins returning blood to the heart in the same ratio in whicn it 

 is carried by the arteries, is proved from the fact that the former 

 are twice as voluminous as the latter. The veins also differ in 

 their internal arrangement from the arteries, the former being 

 furnished, at proper distances, with valves, which guard against a 

 retrograde venous action. 



The Quantity op Blood Contained in the Body 



of a Horse. 



Mr. Perctvall, who is our chief authority on this subject, 

 contends that, for many reasons, the quantity of blood contained 

 in an animal body may be made matter of speculation, but can 

 not, for many reasons, be ascertained with any degree of precision ; 

 for, says he, " if we attempt to draw all the blood out of the body, 

 the animal sinks and dies long before its vessels are evacuated; 

 and as we possess no means of measuring what remains behind, 

 any calculation we may make from the quantity that has flowed 

 must necessarily turn out vague, if not altogether iacorrect." He 

 contends, however, that the following experiment offers a datum, 

 ir guide: 



