1: . DADS VETERINARY MEOICINE AND SURGEKY 
then, venous blood enters the pulmonary tissies. The arteriali 
gation of the blood which follows is a process more esseutin: te 
vital iutegrity 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 snrfice 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—Tl.e 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 ef blocd 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 alco 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 vr HLOOD CONTAINED ™m 18% Bopy 
oF A Horse. 
Mr. PERCIVALL, who ia our chief authori’y on thir. srbject, 
ecntends 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 ue, “if we atzempt 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 liehind, 
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 
w guide: 
