The internal capacity of the ventricles is so modified by the amount of post mortem contraction that it differs widely from the actual capacity during life. The left ventricle of the larger domestic quadrupeds usually admits from 3½ oz. to over 5 oz., while the right ventricle whose walls are so much thinner and more lax will contain double that amount. In the smaller animals about a tenth of these quantities will be admitted.
The weight of the heart too can only be stated as an average or for medium sized animals. In the horse it may be from 4½ lbs. to 9 lbs.; in the ox from 3 lbs. 5 oz. to 4½ lbs.; in the sheep from 5½ oz. to 7 oz.; in the pig from 9½ oz. to 14 oz.; and in the dog from 5 oz. to 7 oz. This statement must be understood to apply to dogs approximating in size to the shepherd’s.
Taking into account the size of the particular animal any considerable deviation from these measurements and weights may be accepted as abnormal. The ratio to the body weight is about:—horse and dog 1:100, ox, sheep and pig 1:220. This necessarily varies with condition—fat or lean.
The pulse offers valuable indications in disease of the heart.
The number of the pulse in healthy full-grown animals may be set down as follows per minute:—horse, 36 to 46; ox, 38 to 42 (with loaded paunch or in a hot stable up to 70); sheep, goat and pig 70 to 80; dog 80 to 100; cat 120 to 140; goose 110; pigeon 136; chicken 140. In old age the pulse is less frequent. This diminution may extend to 5 beats per minute in the larger quadrupeds and to 20 or even 30 in the smaller. Youth and small size again are associated with a greater rapidity of the pulse. The pulse of the foal, at birth, is about three times that of the horse; in the colt of six months it is double; at a year old about one and a half times; and at two years old one and a quarter.
The smaller the animal, caeteris paribus, the more rapid is the pulse. Hot buildings, exertion, fear or any other exciting cause likewise accelerates it. It is more frequent with the nervous temperament, as for example in the English race horse, or the greyhound, than in the dull lymphatic cart horse or mastiff. In advanced pregnancy it is increased in number. In the cow and mare it undergoes a monthly increase of four or five beats per minute after the sixth month. (Delafond)
Independently of these conditions a rapid pulse indicates febrile excitement attendant on active inflammatory or other disease, or a state of weakness and debility. In this last condition the heart beats more frequently to secure a more rapid circulation in the capillary blood vessels, and thus make up to the craving tissues by frequency of contact, what is wanting in the quantity and quality of the nutritive fluid. This point cannot be too much insisted upon, as the fatal doctrine that a rapid pulse indicates force of the circulation is very misleading as to treatment.
The force and character of the pulse differ in the various species. In the horse it is full, moderately tense and elastic. In the ass and mule it is smaller and harder, with an inequality of force in successive beats, and sometimes even a beat is suppressed or imperceptible. In the ox the pulse is full, soft and regular, appearing to roll forward beneath the fingers. In the sheep and goat the pulse is small but with a peculiar quick or sharp beat. The pig’s pulse is said to be firm and hard. That of the dog and cat is firm and hard coming with a sharp impulse against the finger. In the dog, however, successive beats are not always of the same force and an intermission or complete absence of a beat is by no means an indication of disease of the heart or other serious malady. It often attends the slightest excitement in a perfectly healthy animal.
In disease the pulsations may become:—frequent or increased in number; slow or decreased in number; quick or striking with a sharp impulse against the finger; tardy or without sharpness of stroke and as if they rolled slowly past under the finger; full and strong when the impulse is forcible and not easily compressed by the finger; weak, feeble or indistinct in the opposite conditions; small when though perfectly distinct and forcible they are wanting in fulness; hard, when forcible and jarring (this is sometimes called wiry or, if smaller, thready); soft when though the artery may be full the beat is devoid of hardness and easily compressible so as to be unfelt; oppressed when with a full rounded artery, the impulse is jerking though not hard and as if the distended vessels opposed the transmission of the impulse; jerking and receding—leaping, when with empty and flaccid arteries the pulse seems to leap forward with each beat of the heart—(this pulsation may be visible to the eye in the carotids); intermittent when after a number of beats at regular intervals there is a complete pause extending over that period of time which would have been occupied by a full beat; unequal when some beats are strong and others weak; irregular when without any distinct intermission for a period equal to that of a single beat, the intervals between successive beats are of varying length. The pulse further has a peculiar thrill or tremor in states of great debility with deficiency of blood and imperfect filling of the vessels.
Of these the leaping, the intermittent, the unequal and the irregular pulses are of special importance in their bearing on heart diseases.