Horses usually void urine five to seven times a day, and pa.s.s from 4 to 7 quarts. Disease may be shown by increase in the number of voidings or of the quant.i.ty. Frequent urination indicates an irritable or painful condition of the bladder or urethra or that the quant.i.ty is excessive.

In one form of chronic inflammation of the kidneys (interst.i.tial nephritis) and in polyuria the quant.i.ty may be increased to 20 or 30 quarts daily. Diminution in the quant.i.ty of urine comes from profuse sweating, diarrhea, high fever, weak heart, diseased and nonsecreting kidneys, or an obstruction to the flow.

The urine of the healthy horse is a pale or at times a slightly reddish yellow. The color is less intense when the quant.i.ty is large, and is more intense when the quant.i.ty is diminished. Dark-brown urine is seen in azoturia and in severe acute muscular rheumatism. A brownish-green color is seen in jaundice. Red color indicates admixture of blood from a bleeding point at some part of the urinary tract, usually in the kidneys.

The urine of the healthy horse is not clear and transparent. It contains mucus, which causes it to be slightly thick and stringy, and a certain amount of undissolved carbonates, causing it to be cloudy. A sediment collects when the urine is allowed to stand. The urine of the horse is normally alkaline. If it becomes acid the bodies in suspension are dissolved and the urine is made clear. The urine may be unusually cloudy from the addition of abnormal const.i.tuents, but to determine their character a chemical or microscopic examination is necessary. Red or reddish flakes or clumps in the urine are always abnormal, and denote a hemorrhage or suppuration in the urinary tract.

The normal specific gravity of the urine of the horse is about 1.040. It is increased when the urine is scanty and decreased when the quant.i.ty is excessive.

Acid reaction of the urine occurs in chronic intestinal catarrh, in high fever, and during starvation. Chemical and microscopic tests and examinations are often of great importance in diagnosis, but require special apparatus and skill.

Other points in the examination of a sick horse require more discussion than can be afforded in this connection, and require special training on the part of the examiner. Among such points may be mentioned the examination of the organs of special sense, the examination of the blood, the microscopic examination of the secretions and excretions, bacteriological examinations of the secretions, excretions, and tissues, specific reaction tests, and diagnostic inoculation.

FUNDAMENTAL PRINCIPLES OF DISEASE.

By RUSH SHIPPEN HUIDEKOPER, M. D., VET.

[Revised by Leonard Pearson, B. S., V. M. D.]

ANIMAL TISSUES.

The nonprofessional reader may regard the animal tissues, which are subject to inflammation, as excessively simple structures, as similar, simple, and fixed in their organization as the joists and boards which frame a house, the bricks and iron coils of pipe which build a furnace, or the stones and mortar which make the support of a great railroad bridge. Yet while the principles of structure are thus simple, for the general understanding by the student who begins their study the complete appreciation of the shades of variation, which differentiate one tissue from another, which define a sound tendon or a ligament from a fibrous band--the result of disease filling in an old lesion and tying one organ with another--is as complicated as the nicest jointing of Chinese woodwork, the building of a furnace for the most difficult chemical a.n.a.lysis, or the construction of a bridge which will stand for ages and resist any force or weight.

All tissues are composed of certain fundamental and similar elements which are governed by the same rules of life, though at first glance they may appear to be widely different. These are (a) amorphous substances, (b) fibers, and (c) cells.

(a) Amorphous substances may be in liquid form, as in the fluid of the blood, which holds a vast amount of salts and nutritive matter in solution; or they may be in a semiliquid condition, as the plasma which infiltrates the loose meshes of connective tissue and lubricates the surface of some membranes; or they may be in the form of a glue or cement, fastening one structure to another, as a tendon or muscle end to a bone; or, again, they hold similar elements firmly together, as in bone, where they form a stiff matrix which becomes impregnated with lime salts. Amorphous substances, again, form the protoplasm or nutritive element of cells or the elements of life.

(b) Fibers are formed of elements of organic matter which have only a pa.s.sive function. They can be a.s.similated to little strings, or cords, tangled one with another like a ma.s.s of waste yarn, woven regularly like a cloth, or bound together like a rope. They are of two kinds--white connective tissue fibers, only slightly extensible, pliable, and very strong, and yellow elastic fibers, elastic, curly, ramified, and very dense. These fibers once created require the constant presence of fluids around them in order to retain their functional condition, as a piece of harness leather demands continual oiling to keep its strength, but they undergo no change or alteration in their form until destroyed by death.

(c) Cells, which may even be regarded as low forms of life, are ma.s.ses of protoplasm or amorphous living matter, with a nucleus and frequently a nucleolus, which are capable of a.s.similating nutriment or food, propagating themselves either into others of the same form or into fixed cells of another outward appearance and different function but of the same const.i.tution. It is simply in the mode of the grouping of these elements that we have the variation in tissues, as (1) loose connective tissue, (2) aponeurosis and tendons, (3) muscles, (4) cartilage, (5) bones, (6) epithelia and endothelia, (7) nerves.

(1) Loose connective tissue forms the great framework, or scaffolding, of the body, and is found under the skin, between the muscles surrounding the bones and blood vessels, and entering into the structures of almost all the organs. In this the fibers are loosely meshed together like a sponge, leaving s.p.a.ces in which the nutrient fluid and cells are irregularly distributed. This tissue we find in the skin, in the s.p.a.ces between the organs of the body where fat acc.u.mulates, and as the framework of all glands.

(2) Aponeurosis and tendons are structures which serve for the termination of muscles and for their contention, and for the attachment of bones together. In these the fibers are more frequent and dense, and are arranged with regularity, either crossing each other or lying parallel, and here the cells are found in minimum quant.i.ty.

(3) In the muscles the cells lie end to end, forming long fibers which have the power of contraction, and the connective tissue is in small quant.i.ty, serving the pa.s.sive purpose of a band around the contractile elements.

(4) In cartilage a ma.s.s of firm amorphous substance, with no vascularity and little vitality, forms the bed for the chondroplasts, or cells of this tissue.

(5) Bone differs from the above in having the amorphous matter impregnated with lime salts, which gives it its rigidity and firmness.

(6) Epithelia and endothelia, or the membranes which cover the body and line all its cavities and glands, are made up of single or stratified and multiple layers of cells bound together by a glue of amorphous substance and resting on a layer composed of fibers. When the membrane serves for secreting or excreting purposes, as in the salivary glands or the kidneys, it is usually simple; when it serves the mechanical purpose of protecting a part, as over the tongue or skin, it is invariably multiple and stratified, the surface wearing away while new cells replace it from beneath.

(7) In nerves, stellate cells are connected by their rays to each other, or to fibers which conduct the nerve impressions, or they act as receptacles, storehouses, and transmitters for them, as the switch-board of a telephone system serves to connect the various wires.

All these tissues are supplied with blood in greater or less quant.i.ty.

The vascularity depends upon the function which the tissue is called upon to perform. If this is great, as in the tongue, the lungs, or the sensitive part of the hoof, a large quant.i.ty of blood is required; if the labor is a pa.s.sive one, as in cartilage, the membrane over the withers, or the tendons of the legs, the vessels only reach the periphery, and nutrition is furnished by imbibition of the fluids brought to their surface by the blood vessels.

Blood is brought to the tissues by arterioles, or the small terminations of the arteries, and is carried off from them by the veinlets, or the commencement of the veins. Between these two systems are small, delicate networks of vessels called capillaries, which subdivide into a veritable lacework so as to reach the neighborhood of every element.

In health the blood pa.s.ses through these capillaries with a regular current, the red cells or corpuscles floating rapidly in the fluid in the center of the channel, while the white or ameboid cells are attracted to the walls of the vessels and move very slowly. The supply of blood is regulated by the condition of repose or activity of the tissue, and under normal conditions the outflow exactly compensates the supply. The caliber of the blood vessels, and consequently the quant.i.ty of blood which they carry, is governed by nerves of the sympathetic system in a healthy body with unerring regularity, but in a diseased organ the flow may cease or be greatly augmented. In health a tissue or organ receives its proper quant.i.ty of blood; the nutritive elements are extracted for the support of the tissue and for the product, which the function of the organ forms. The force required in the achievement of this is furnished by combustion of the hydrocarbons and oxygen brought by the arterial blood, then by the veins this same fluid pa.s.ses off, less its oxygen, loaded with the waste products, which are the result of the worn-out and disintegrated tissues, and of those which have undergone combustion. The foregoing brief outline indicates the process of nutrition of the tissues.

Hypernutrition, or excessive nutrition of a tissue, may be normal or morbid. If the latter, the tissue becomes congested or inflamed.

CONGESTION.

Congestion is an unnatural acc.u.mulation of blood in a part. Excessive acc.u.mulation of blood may be normal, as in blushing or in the red face which temporarily follows a violent muscular effort, or, as in the stomach or liver during digestion, or in the lungs after severe work, from which, in the latter case, it is shortly relieved by a little rapid breathing. The term congestion, however, usually indicates a morbid condition, with more or less lasting effects. Congestion is active or pa.s.sive. The former is produced by an increased supply of blood to the part, the latter by an obstacle preventing the escape of blood from the tissue. In either case there is an increased supply of blood, and as a result increased combustion and augmented nutrition.

ACTIVE CONGESTION.

Active congestion is caused by--

(1) _Functional activity._--Any organ which is constantly or excessively used is habituated to hold an unusual quant.i.ty of blood; the vessels become dilated; if overstrained the walls become weakened, lose their elasticity, and any sudden additional quant.i.ty of blood engorges the tissues so that they can not contract, and congestion results. Example: The lungs of a race horse, after an unusual burst of speed or severe work, in damp weather.

(2) _Irritants._--Heat and cold, chemical or mechanical. Any of these, by threatening the vitality of a tissue, induce immediately an augmented flow of blood to the part to furnish the means of repair--a hot iron, frostbites, acids, or a blow.

(3) _Nerve influence._--This may produce congestion either by acting on the part reflexly or as the result of some central nerve disturbance affecting the branch which supplies a given organ.

(4) _Plethora and sanguinary temperament._--Full-blooded animals are much more predisposed to congestive diseases than those of a lymphatic character or those in an anemic condition. The circulation in them is forced to all parts with much greater force and in large quant.i.ties. A well-bred, full-blooded horse is much more subject to congestive diseases than a common, coa.r.s.e, or old, worn-out animal.

(5) _Fevers._--In fever the heart works more actively and forces the current of blood more rapidly; the tissues are weakened, and it requires but a slight local cause at any part to congest the structures already overloaded with blood. Again, in certain fevers, we find alteration of the blood itself, rendering it less or more fluid, which interferes with its free pa.s.sage through the vessels and induces a local predisposition to congestion.

(6) _Warm climate and summer heat._--Warmth of the atmosphere relaxes the tissues; it demands of the animals less blood to keep up their own body temperature, and the extra quant.i.ty acc.u.mulates in the blood-vessel system. It causes sluggishness in the performance of the organic functions, and in this way it induces congestion, especially of the internal organs. So we find founders, congestive colics, and staggers more frequent in summer than in winter.

(7) _Previous congestion._--Whether the previous congestion of any organ has been a continuous normal one--that is, a repeated functional activity--or has been a morbid temporary overloading, it always leaves the walls of the vessels weakened and more predisposed to recurrent attacks from accidental causes than are perfectly healthy tissues. Thus a horse which has had a congestion of the lungs from a severe drive is liable to have another attack from even a lesser cause.

The alterations of congestion are distention of the blood vessels, acc.u.mulation of the cellular elements of the blood in them, and effusion of a portion of the liquid of the blood into the fibrous tissues which surround the vessels. When the changes produced by congestion are visible, as in the eye, the nostril, the mouth, the genital organs, and on the surface of the body in white or unpigmented animals, the part appears red from the increase of blood; it becomes swollen from the effusion of liquid into the spongelike connective tissues; it is at times more or less hot from the increased combustion; the part is frequently painful to the animal from pressure of the effusion on the nerves, and the function of the tissue is interfered with. The secretion or excretion of glands may be augmented or diminished. Muscles may be affected with spasms or may be unable to contract. The eyes and ears may be affected with imaginary sights and sounds.

Pa.s.sIVE CONGESTION.

Pa.s.sive congestion is caused by interference with the return of the current of blood from a part.

Old age and debility weaken the tissues and the force of the circulation, especially in the veins, and r.e.t.a.r.d the movement of the blood. We then see horses of this cla.s.s with stocked legs, swelling of the sheath of the p.e.n.i.s or of the milk glands, and of the under surface of the belly. We find them also with effusions of the liquid parts of the blood into the lymph s.p.a.ces of the posterior extremities and organs of the pelvic cavity.

Tumors or other mechanical obstructions, by pressing on the veins, r.e.t.a.r.d the flow of blood and cause it to back up in distal parts of the body causing pa.s.sive congestion.

The alterations of pa.s.sive congestion, as in active congestion, consist of an increased quant.i.ty of blood in the vessels and an exudation of its fluid into the tissues surrounding them, but in pa.s.sive congestion we have a dark, thick blood which has lost its oxygen, instead of the rich, combustible blood rich in oxygen which is found in active congestion.

The termination of congestion is by resolution or inflammation. In the first case, the choked-up blood vessels find an outlet for the excessive quant.i.ty of blood and are relieved; the transuded serum or fluid of the blood is reabsorbed, and the part returns almost to its normal condition, with, however, a tendency to weakness predisposing to future trouble of the same kind. In the other case further alterations take place, and we have inflammation.

INFLAMMATION.