38 
Organs of the Animal Body : their Forms and Uses. 
be done by an expert dissector. The practical man must there- 
fore accept the statement that the arteries go to all parts of the 
body from the ventricles, to carry good blood for their support 
and repair, or bad blood to be purified. The veins begin with 
small branches, which join together as they get nearer the heart, 
until at last there are only two large ones, which receive the 
blood after it has done its work, and become mixed with various 
impurities, and take it into the right side of the heart. 
Of the action of the heart and blood-vessels everybody has 
some general ideas. It is well known that the heart is the organ 
which drives the blood over the body, and experiments have 
shown that the force which it can exercise is sufficient for this 
purpose. When the left ventricle of the organ contracts, the 
blood which it contains is forced into the arteries already full of 
the fluid, and the whole mass of blood is moved onwards with a 
bound which distends the elastic vessels, and is felt all over the 
system in the beats of the pulse, which take place with remark- 
able regularity when the animal is at rest and in health, but 
undergo great changes in number and force under excitement, 
or during the course of disease. 
For practical purposes the following numbers may be taken as 
generally correct. Number of pulse in a minute : horse, 36 ; 
ox, 55 ; sheep, 75. 
The risht ventricle of the heart contracts at the same time 
as the left one, but with less force, as it only has to send the 
blood which has already gone over the body and given up 
a good deal of its best material, taking in exchange a lot of 
bad, to the lungs, where it can get rid of the waste matters, 
carbonic acid, and other products of combustion, and get a 
fresh supply of oxygen, before it is returned to the left side 
of the heart to be pumped over the body. This movement of 
the blood from the right side of the heart through the lungs 
to the left side, is described as the LESSER CIKCULATION. The 
pumping of the fluid from the left side of the heart through the 
vessels of the system back to the right side of the organ is 
the " GREATER CIRCULATION." 
From the minute hair-like tubes (capillaries) in which arteries 
end, the portion of the blood which contains all the nutritive 
elements is constantly leaking into the tissue, which use what 
amount of it they require, while the rest is taken up into the 
absorbent vessels (lymphatics), and again is poured into the blood 
on its return to the heart through the veins by the thoracic 
duct (see h, Fig. 23, p. 36). The blood is therefore always 
giving up something to the tissues, and always getting some- 
thing back again from the absorbents, the total result being 
that the blood-vessels get rid of the whole quantity of blood 
