66 KENNEL DISEASES. 
Ample exercise is of great importance, but it must be properly regulated ; not 
be too severe at first, and increased gradually, for otherwise the consequences 
might be disastrous. 
HEART-DISEASES. 
The heart is a hollow, muscular organ, the engine of circulation, or the for- 
cing-pump which keeps the current of blood in motion. It is partitioned to con- 
tain four chambers or cavities. The two on each side communicate with each 
other, but there is no connection between the sides. Each chamber has two 
openings, an inlet and an outlet; and these are provided with valves, which open 
to admit the entrance of the blood, and close tightly to prevent its return. The 
passage of the blood through the heart is easily described. It returns by the 
veins from the different parts of the body and enters the upper cavity on the right 
side. When that is filled its walls contract and impel its contents into the 
lower cavity; the walls of which in turn contract and force the blood into and 
along the great artery of the lungs. That blood, which was dark and impure 
when it entered the lungs, soon leaves them bright and pure, and returns to the 
heart; this time entering it on the left side. From the upper to the lower cavity 
it passes, as on the other side, and is then delivered into the arteries and dis- 
tributed throughout the body. Thus the movement of the blood through the 
- heart is accomplished by alternate contractions and relaxations of its muscular 
walls, and each of these successive movements is called a beat or pulsation. 
The base of this vital organ is so attached that it is securely held in place, while 
its tip or apex is freely movable and knocks gently against the inside of the 
chest. To avoid friction it is enclosed in a sack called the pericardium, formed 
by two layers of a thin membrane, the inner surfaces of which are as smooth as 
satin, and ‘at all times made slippery by a fluid that is poured upon them. 
If the ear be placed to the chest directly over the apex of the heart, when 
the beat is felt two sounds will be heard. These are believed to be caused by 
the closure of the valves. The first is louder and stronger than the second. 
This and other differences in character between them are attributed to the differ- 
ences in the arrangement of the two sets of valves. In disease of the heart, 
during the course of or following which either of the valves become defective, 
the heart-sounds in question are changed. There is a slight difference in the 
sound made by the shutting of the valves, due to imperfect closure of them, or 
an unnatural sound is added; and this is produced by the current of blood as 
it passes through one or more of the orifices of the heart at which the valves are 
located, and is in consequence of those openings being diminished in size. That 
narrowing of the openings is one of the products of disease, and generally due 
