lO:. D4D1)S ViniRItAlY MKOUINfi MiU SUHGEJCY 



tiieu, venous bio )d enters the pulmonary lissies. Tlie artoriali 

 latioE o:' the blood which follows is a proceijs more eu&tiitiui to 

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

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

 unless the blood be oxygenized. 



The pulmonary arteries branch off into minute ramifications on 

 the surf ice of the air-ceils of the lungs, and where th.(ise minute 

 division;? terminate others commence, termed venous radicles, 

 which ultimately become large veins. By the pulmonary veins 

 the oxygenized blood is returned to ihc hift auricle and ventricle 

 of the heart. This route of the blooii t'l cm he:irt to lungs, and back 

 again from lungs to heart, is termed tlie legrfer circulation. The 

 left ventricle delivers the blood into the gn^t aorta, and thence 

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



Difference between Veins and Arteri&8. — The veins difler from 

 arteries in being less dense, having no muscular nor iigamentar) 

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

 tight collars and tight-fitting harness and circiugles, wliich are ai>t 

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

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

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

 are twice as voluminous as the latter. The vei'.is alf.o differ in 

 their internal arrangement from the aiterie**, the foriuer being 

 furnished, at proper distances, with valves, which guai'd against a 

 retrograde venous action. 



The Quantity oy JiLOCD Cont/iskt in i:n« .^dy 



OP A IIOltSE. 



Mr. PiiUCiVALi., who is our chief authoii.y on thii, subject, 

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

 ia ari animal body may be made matttr of speculation, but can 

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

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

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

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

 any calculation we may make from the quantity that has floive«l 

 2nii?t ncc(«yarily turn out vague, if not altogether iacorr«!ct." He 

 contends, howover, that the following ijxperiment offers a datum 

 >r guide: 



