310 THE HORSE. 
line ; those of the ass being still smaller, though only slightly so. As in 
all of the mammalia but the camels, these bodies are circular flattened 
discs, and are of the same size (nearly) in all animals of the same species, 
whatever may be the age or sex. According to Messrs. Prevost and 
Dumas, the blood of the horse contains less solid matter than that of man, 
in the proportion of 9°20 to 12°92 in 1,000 parts. The temperature is 
also lower by about two degrees of the centigrade thermometer, the pulse 
slower in the proportion of 56 to 72, and the respirations 16 per minute’ 
against 18 in our own species. ‘The shade of colour in the red corpuscles 
depends upon the proportion of carbonic acid and oxygen combined with 
them. If the former preponderates, a deep purple-red is developed, known 
as that of venous blood; while a liberal supply of oxygen develops the 
bright scarlet peculiar to arterial blood. The saline matters dissolved in 
the liquor sanguinis consist of the chlorides of sodium and potassium 
(which comprise more than one half of the whole salts), the tribasic 
phosphate of soda, the phosphates of magnesia and lime, sulphate of soda, 
and a little of the phosphate and oxyde of iron. 
GENERAL PLAN OF THE CIRCULATION. 
THE BLOOD IS CIRCULATED through the body, for the purposes of nutri- 
tion and secretion, by means of one forcing pump, and through the lungs, 
for its proper aeration, by another; the two being united to form the 
heart. This organ is therefore a 
compound machine, though the two 
pumps are joimed together, so as to 
appear to the casual observer to be 
one single organ. In common lan- 
guage, the heart of the mammalia is 
said to have two sides, each of which 
is a forcing pump; but the blood, 
before it passes from one side to the 
other, has to circulate through one 
or other of the sets of vessels found 
in the general organs of the body, 
and in the lungs, as the case may 
be. This is shown at Fig. 38, where 
the blood, commencing with the 
capillaries on the general surface 
at A, passes through the veins 
which finally end in the vena cava 
(B), and enters the right auricle 
Fic. 3.—PLAN OF THE CIRCULATION, 
A. Capillaries on the general surface. 
3. Vena cava. 
C. Right auricle. (C). From this it is pumped into 
D. Right ventricle. ; : t 
1. Pulmonary artery. the right ventricle (D), which, con- 
F. Capillaries of the lungs, uniting to form tracting in its turn, forces it. on into 
the pulmonary veins, which enter 
G. The left auricle. the pulmonary artery (E), spreading 
L The sonia dividing into smaller OUb upon the lining membrane of 
arteries, and united with the capillaries the lungs, to form the capillaries 
J. The trunk of the aorta anterior. of that organ at F, from which it 
is returned to the left auricle (G) 
through the pulmonary veins. rom the left auricle it is driven on to the 
left ventricle; and this, by its powerful contractions, forces the blood 
through the aorta (I), and the arteries of the whole body, to the capil- 
laries (A), from which the description commenced. But though this organ 
