Part 23

Diagram illustrating the circulation of the blood. The arrows indicate the direction in which the blood flows. The valves of the heart, situated between the right auricle and ventricle, and left auricle and ventricle, and between the ventricles and large arteries, are represented by curved lines. These valves are intended to prevent the flow of blood in a direction contrary to that indicated by the arrows.

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NONCONTAGIOUS DISEASES OF THE ORGANS OF RESPIRATION.

By WILLIAM HERBERT LOWE, D. V. S.

DIAGNOSIS.

In the determination of disease in the human being the physician, in making his diagnosis, is aided by both subjective and objective symptoms, but the veterinary physician, in a very large majority of cases, is obliged to rely almost solely upon objective symptoms, and perhaps in no class of diseases is this more true than in the exploration of those under consideration. This condition of affairs has a strong tendency to develop observation and discernment in the veterinarian, and not infrequently do we find that the successful veterinary practitioner is a very accurate diagnostician. In order to make a differential diagnosis, however, it is not only necessary to know the structure and functions of the organs in health, but to adopt a rigid system of details of examination, without which successful results can not be reached.

History.--The history of a case should always be ascertained so far as possible. The information obtained is sometimes unsatisfactory and not to be depended upon, but even when this is the case it is advisable to weigh the evidence from every point of view.

In connection with the history of every case it is always of primary importance to ascertain the cause of illness. A knowledge of the origin and development of a disease is important, both in making a diagnosis and in formulating the treatment. Exposure to cold and dampness is frequently the exciting cause of affections of the organs of respiration.

The experienced practitioner is always sure to ascertain whether the particular animal he is called on to attend is the only one in the stable or on the premises that is similarly affected. If several animals are similarly affected, the disease may have a common cause, which may or may not be of an infectious nature.

Another thing that the experienced practitioner ascertains is what previous treatment, if any, the animal has had. Medicine given in excessive doses sometimes produces symptoms resembling those of disease.

The hygienic and sanitary conditions must always be considered in connection with the cause as well as the treatment of disease. Much of the disease which occurs in large dairies and elsewhere could be prevented if owners and those in charge of animals had proper regard for the fundamental laws of animal hygiene and modern sanitation. Disregard for these laws is the cause of most of the diseases under consideration in this chapter.

Attitude and general condition.--The feeling of pain in animals suffering from serious affections of the organs of respiration is expressed to the close observer in no uncertain language--by their flinching when the painful part is touched; by the care with which they move or lie down; by walking or standing to "favor" the part; by the general attitude and expression of the eye; by the distress and suffering apparent in the face; and by other evidences.

The general physical condition and attitude of the sick animal tell the careful observer much that aids him in making a diagnosis and prognosis. Cows suffering from affections of the organs of respiration usually assume a position or attitude that is characteristic, well known to experienced stockmen, as well as to veterinarians. When an animal has a fever or is suffering from an inflammation, the skin is one of the first parts to undergo a change that is apparent to the average observer, for it soon loses its elasticity and tone, and the hair becomes dry and staring.

From the general condition or state of nutrition one is able to judge the effect that the disease has already had upon the animal and to estimate the strength remaining available for its restoration to health; from the degree of emaciation one can approximate the length of time the animal has been ill. The age and breed of the animal, as well as its constitution and temperament, are among the things that have to be taken into account in making a diagnosis and in overcoming the disease.

The mucous membrane.--The mucous membrane should in all cases be examined. It can be readily seen by everting the eyelids or by an inspection of the lining membrane of the nostrils.

Paleness of the mucous membrane indicates weak circulation or poor blood and may result from disease, hemorrhage, or from inappropriate feed.

In healthy animals increased redness of the mucous membrane occurs from pain, excitement, or severe exertion, and in such instances is always transitory. In certain pathological conditions, such as fevers and inflammation, this condition of the mucous membrane will also be found. The increased redness of the mucous membrane lasts during the duration of the fever or inflammation.

A bluish or blue mucous membrane indicates that the blood is imperfectly oxidized and contains an excess of carbon dioxid, and is seen in serious diseases of the respiratory tract, such as pneumonia, and in heart failure.

The secretions.--The secretions may be diminished, increased, or perverted. In the early stage of an inflammation of a secretory organ its secretion is diminished. In the early stage of pleurisy the serous membrane is dry, and as the disease advances the membrane becomes unnaturally moist. The products of secretion are sometimes greatly changed in character from the secretion in health, becoming excessively irritant and yielding evidence of chemical and other alterations in the character of the secretion.

Cough.--Cough depends upon a reflex nervous action and may be primary when the irritation exists in the lungs or air passages, or secondary when caused by irritation of the stomach, intestines, or other parts having nervous communications with the respiratory apparatus. A cough is said to be dry, moist, harsh, hollow, difficult, paroxysmal, suppressed, sympathetic, etc., according to its character. It is a very important symptom, often being diagnostic in diseases of the respiratory organs, but this is a subject, however, which can be more satisfactorily treated in connection with the special diseases of the organs in question.

Respiration.--In making an examination of an animal observe the depth, frequency, quickness, facility, and the nature of the respiratory movements. They may be quick or slow, frequent or infrequent, deep or imperfect, labored, unequal, irregular, etc., each of which indications has its significance to the experienced veterinarian.

Sleep, rumination, pregnancy in cows, etc., modify the respiratory movements even in health. Respiration consists of two acts--inspiration and expiration. The function of respiration is to take in oxygen from the atmospheric air, which is essential for the maintenance of life, and to exhale the deleterious gas known as "carbon dioxid."

The frequency of the respiratory movements is determined by observing the motions of the nostrils or of the flanks. The normal rate of respiration for a healthy animal of the bovine species is from 15 to 18 times a minute. The extent of the respiratory system renders it liable to become affected by contiguity to many parts and its nervous connections are very important.

Rapid, irregular, or difficult breathing is known as dyspnea, and in all such cases the animal has difficulty in obtaining as much oxygen as it requires. Among the conditions that give rise to dyspnea may be mentioned restricted area of active lung tissue, owing to the filling of portions of the lungs with inflammatory exudate, as in pneumonia; painful movements of the chest, as in rheumatism or pleurisy; fluid in the chest cavity, as in hydrothorax; adhesions between the lungs and chest walls; compression of the lungs or loss of elasticity; excess of carbon dioxid in the blood; weakness of the respiratory passages; tumors of the nose and paralysis of the throat; swellings of the throat; foreign bodies and constriction of the air passages leading to the lungs; fevers, etc.

As already stated, it is only the careful and constant examination of animals in health that will enable one properly to appreciate abnormal conditions. One must become familiar with the frequency and character of the pulse and of the respirations and know the temperature of the animal in health, before changes in abnormal conditions can be properly appreciated.

Temperature.--The temperature should be taken in all cases of sickness. Experienced practitioners can approximate the patient's temperature with remarkable accuracy, but I strongly recommend the use of the self-registering clinical thermometer, which is a most valuable instrument in diagnosing diseases. (See Pl. III, fig. 1.) It is advisable to get a tested instrument, as some thermometers in the market are inaccurate and misleading. The proper place to insert the thermometer is in the rectum, where the instrument should be rested against the walls of the cavity for about three minutes. The normal temperature of the bovine is 101∞ to 102∞ F., which is higher than that of the horse. A cow breathes faster, her heart beats faster, and her internal temperature is higher than that of the horse. Ordinary physiological influences--such as exercise, digestion, etc.--give rise to slight variations of internal temperature; but if the temperature rises two or three degrees above the normal some diseased condition is indicated.

Pulse.--The pulse in a grown animal of the bovine species in a state of good health beats from 45 to 55 times a minute. Exercise, fright, fear, excitement, overfeeding, pregnancy, and other conditions aside from disease may affect the frequency and character of the pulse. It assumes various characters according to its rapidity of beat, frequency of occurrence, resistance to pressure, regularity, and perceptibility. Thus we have the quick or slow, frequent or infrequent, hard or soft, full or imperceptible, large or small pulse, the character of each of which may be determined from its name; also that known as the intermittent, either regular or irregular. We may have a dicrotic, or double, pulse; a thready pulse, which is extremely small and scarcely perceptible; the venous, or jugular, pulse; the "running down" pulse, and so on. (See p. 76.)

In cattle the pulse is conveniently felt over the submaxillary artery where it winds around the lower jawbone, just at the lower edge of the flat muscle on the side of the cheek. If the cow is lying down the pulse may be taken from the metacarpal artery on the back part of the fore fetlock. The pulsations can be felt from any superficial artery, but in order to ascertain the peculiarities it is necessary to select an artery that may be pressed against a bone.