General Diseases Common to all Animals.
Morbid State of the Blood. A nutritive fluid circulates through the tissues of all organized life. This liquid, which is essential to life, is known as the sap in plants, and the blood in animals. The sap is probably simply nutritive; the liquid flesh, as the blood has been called, is a nutrient and something more, for it is also the means
By which some of the used up materials are removed from the system, as it flows through the liver, kidneys, lungs, etc. The characteristics of the living animal organism are ceaseless change and ceaseless waste. Directly it begins to live it begins to die. In the blood, as in the different tissues, the process of decay and regeneration, of destruction and reconstruction, only terminate with the extinction of vitality. During action the tissues waste; during repose they are nourished and the waste repaired. Hence an animal must have pure air, good sound food in proper quantity, pure soft water, and a proper amount of exercise, rest, and sleep, in order that he may have a due supply of good nutrient blood, to be distributed to the various tissues for their healthy, proper nourishment. "The blood is the life"; good blood is healthy life.
In early life the amount of this nutrition absorbed by the various tissues of the body is greater than the expenditure of used up tissues; hence there is a gradual, healthy increase in weight. But in old age this operation is reversed, until the means of repair are at length exhausted; used up material is thrown off, new healthy material does not take its place, and the animal dies of old age.
Something of the same thing happens in disease, the early operation of which is to upset the normal equilibrium between supply and waste; the tissues of the body continue to waste, in an excess, which is not removed; useless or poisonous agents then become generated within the body, from this retention, and sickness of more or less moment results.
Life is only to be maintained by the circulation of pure arterial blood; and whether no blood circulates through the arteries or only
that which has become impure and contaminated from various causes, the result will sooner or later be the same; the death of the animal.
When no blood circulates the death takes place from fainting (syncope); and this is of two kinds. First, anemia, when there is a want of the due supply of blood to the heart, as is witnessed in fatal hemorrhages. Second, by asthenia, when there is a failure in the contractile power of the heart, seen to occur from the action of certain poisons, intense terror, from overdoses of electricity, concussion of the brain, as well as certain forms of apoplexy. Death may also take place from a mixture of these two causes, as may be particularly noticed in fatal cases of starvation and lingering disorders.
Death may also take place from the circulation of venous blood through the arteries, and this may result in two ways: suffocation (apnea) when the access of air to the lungs is prevented, as in drowning, strangulation, choking, immobility of the respiratory muscles from a bad case of wind colic, pneumonia, when a large portion of the lung tissue has become solidified, dropsies into the cavity of the chest, etc.; and com, in which, although the air passages are free, the muscular movements required for respiration cease, owing to insensibility produced by some trouble with the brain, as milk fever in cows; cerebrospinal meningitis in horses and dogs; some forms of distemper in dogs; as well as in some other disorders not so frequently met with.
Thus in death by apnea there is, successively, impeded respiration, the circulation of no oxygenated blood, and insensibility; while in coma, the order of the phenomena is reversed; there is first insensibility, followed by a cessation of the muscular movements of the chest walls; and the consequent circulation of blood which has not been made "arterial," i.e., oxygenated.
The blood may be described as being an albuminous fluid, charged with various salts holding the elements of fibrin in solution, and containing both red and white globules (corpuscles). Its specific gravity is high; the extremes, compatible with health, will vary from 1050 to 1059, as measured with distilled water at 1000. The gravity is diminished by bleeding, amnesia, or albuminuria; While it is increased by conditions inducing excessive watery discharges either from the bowels or kidneys. It is most probable that the average relative weight of the blood to that of the body is about as one to fourteen, the maximum being found as the digestion of a hearty mea". is drawing to a close. The blood vessels of an healthy adult horse, of one thousand pounds weight, probably contain about seventy-two pounds of blood
The blood receives matter from three sources: the atmospheric air through the lungs; the digestion which takes place in the alimentary canal;. and the secondary digestion, as that process has been called, by which the waste tissues of the body are absorbed, to be discharged from the economy.
In return it furnishes material for building up the tissues, for forming the secretions, while it also warms every part of the body. Hence whatever interferes with the process of digestion, or respiration, with the excretory organs, as the bowels, liver, kidneys, and skin, as well as the healthy condition of the nervous system, will affect the composition of the blood and so induce a disorder of more or less gravity.
Plethora Congestion. Is fullness of blood. Men the blood merely exists in too great a quantity in one or more of the organs or tissues, there is said to be a partial plethora or congestion of the organ or tissue affected, in which case there is no increase in the total amount of blood or any of its constituents in the body.
If an organ or a part of any living body becomes irritated from any cause, as from proper exercise, there is an increased flow of blood to that part. If the irritation is carried beyond that which is natural and proper to the part, as from "catching cold" in the lungs, or from a strain of a tendon, the blood vessels then ' become unable to pass the blood through them properly; as a result, swelling takes place, that is, there is an active congestion of the part. This condition, after a time, either decreases little by little (resolution), ends in slight hemorrhage into the immediate tissues from rupture of the overloaded vessels, or passes on to inflammation.
Again, the circulation of the blood through a part may be sluggish owing to a want of tone in the walls of the veins; this gives rise to what is called a passive congestion there. When the return of blood through a vein, on its way to the heart, is impeded by any pressure upon the vessel from without, it is described as a mechanical congestion. Such a condition may be brought about by a badly fitting collar on a draft horse, or by tying a string around a part of the leg or tail, as is not infrequently done by a mischief maker.
The condition so commonly found in horses, which seem otherwise to be in good health, wherein the legs swell or a swelling appears along the under part of the belly or around the sheath, generally so easily removed by exercise, is a passive congestion due to want of tone of the veins of the part.
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