These are the seat of congestions, neoplasms, and parasites, including pentastoma, actinomycosis, tubercle, glanders, etc., which will be treated under their respective headings.
PARASITES OF THE AIR PASSAGES, LUNGS, AND PLEURA.
Nearly all the domestic animals are subject to parasites of the lower air passages. These give rise to verminous bronchitis in cattle, sheep, horses, swine, goats and camels, to gapes in birds, and to pulmonary acariasis in fowls. The lungs and pleura are invaded by distomum, echinococcus, cysticercus, aspergillus, etc. (See parasites).
DISEASES OF THE HEART AND ORGANS OF CIRCULATION.
Susceptibility in different genera. Reasons for partial immunity of the quadruped, special and general causes in quadrupeds, violent, forced work, fatty degeneration, swallowing of pointed metallic bodies, difficult diagnosis in the animal. Position of the heart in the horse, ox, sheep, pig, carnivora, birds. Structure of the heart as a pump. Results of imperfect structure or action. Heart walls. Table of size of the heart. Capacity. Weight. Pulse in each healthy genus, according to age, size, environment, temperament, proximity to parturition. Morbid conditions of the pulse, frequent, slow, quick, tardy, full, strong, weak, feeble, indistinct, small, hard, wiry, thready, oppressed, leaping and receding, intermittent, unequal, irregular, anæmic, venous. Percussion. Palpitation. Auscultation. Healthy sounds. Morbid sounds, in unusual place, force, intensity, rythm, repetition of 1st sound, of 2nd sound. Murmurs, synchronance with given stages of heart movement, their significance, pericardial murmur. General symptoms of heart disease, cold extremities, passive congestions, dropsies of limbs, etc., shortness of breath, venous pulse, vertigo, dulness, sluggishness, corpulence.
The lower animals are perhaps less subject to heart disease than mankind, but the comparative immunity generally assumed for them is far from being a real one. The horizontal position of the quadruped largely obviates that special tax upon the heart demanded by the erect position of man, and especially by the elevated place given to his more ample and vascular brain. Animals too are comparatively free from those mental and moral influences which so largely affect the regularity of the circulation in the human subject. But on the other hand many physical causes of heart disease affect the lower creation equally with their lord, while some undoubtedly operate with special force on the brute. All animals are subject to diseases of the heart as of other internal organs, from exposure; this organ is occasionally involved from its contiguity with other diseased structures or from interdependence of function as we have already seen in certain diseases of the lungs (congestion, broken wind, etc.); the tendency to heart disease frequently runs in a particular family of animals, especially with the rheumatic constitution, which is transmitted from parent to offspring as surely as the color of the skin the turn of the horn or the depth and spring of the rib. The lower animals are further subject to congenital malformations and imperfections and to deposits of morbid material around the heart or in its substance so as to impair its healthy action.
Horses and dogs have special predisposing causes in the violent and prolonged exertion to which they are habitually exposed. The quiet sluggish and nonexcitable ox and pig meet with dangers no less real though of a different kind in the overfeeding which induces fatty degeneration of the heart as of other muscular tissues. The larger ruminants are further endangered by their propensity to swallow needles and other sharp pointed bodies which ultimately reach and penetrate the heart.
The prevalence of heart disease in animals may be deduced from the fact that out of 150 horses, oxen and dogs dissected at Montfauçon by Leblanc in 1840, not less than one twentieth presented cardiac lesions. The supposition of an immunity of the lower animals has been largely due to the heavy muscular shoulder of quadrupeds which covers the upper and anterior regions of the heart shutting them out from physical exploration. In man the entire heart and connecting blood vessels are so open to examination that the physician can pronounce with the greatest accuracy not only concerning the existence of disease, but also its precise locality and nature. In the quadruped no such facility is open to us, and veterinarians have too generally refused to face the difficulty, preferring to ignore heart diseases, or still worse seeking to cover their ignorance by the assertion that such affections rarely exist. Now however we not only know that heart diseases are much more frequent in the lower animals than heretofore believed, but that as a general rule they are sufficiently manifested and recognizable by their distinctive symptoms.
Position and exposure of the heart. In the horse the heart has only its apex and a small portion of its left ventricle approached to the surface of the chest, at a point where it is felt to beat behind the left elbow. The apex approaches the surface in the interval between the fifth and sixth ribs and close above the breast bone. The posterior border of the ventricle follows a nearly vertical line upwards from this point, while the anterior border has a direction upward and forward crossing diagonally over the fifth rib. The part of the ventricle exposed extends about three inches upwards from the apex, and is about two inches in its transverse diameter. The great mass of the organ is covered by lung substance.
In the ox about the same extent of heart tissue is exposed. In sheep a portion about an inch in height and one and a half inches in breadth is left uncovered by lung. In the pig the heart is exposed only in a triangular space of about an inch across.