Importance of diseases of the respiratory organs—in horses and dogs.
Proclivity through over-exertion, through extent and delicacy of the
mucosa, through changes of temperature, through weather, through air
pollution, through kind of diet, through change of latitude, through
nervous sympathy, through debilitation of the lung tissue, through
suppression of perspiration, through a high dew point, through
bacteria and other germs, through youth and change of habits.
These are among the most frequent and grave of all affections of the
domestic animals. They are especially important however in the case of
animals that depend on the soundness of their wind. In horses and dogs
accordingly any permanent injury to the organs of respiration will
seriously impair the value, not only because of the diminished
usefulness of the affected animal, but also because of the probable
deterioration of their progeny. The rapid paces demanded of these
animals and the strain to which the respiratory organs are subject are
potent causes of respiratory disorder. In all animals, however, the
extent of the respiratory surface and its extreme delicacy and tenuity
especially predispose it to disease. Hales estimates that the mucous
membrane covering all the air sacs and air cells is, in the calf, no
less than 250 square feet. As the chest of the horse is at least double
that of the calf, and as it contains much less connective tissue, and is
made up of minute air cells from ¹⁄₇₀–¹⁄₂₀₀ inch in diameter and
separated from each other by walls so attenuated that the contained
capillary bloodvessels are equally exposed to the air on both sides, in
two adjacent air cells, the estimate for the average horse must be
considerably above 500 square feet. This membrane, incomparably the most
delicate and susceptible in the animal economy, is constantly in contact
with the air in all its variable conditions, and is necessarily affected
by these variations.
The severe changes of temperature are not without their influence on
this sensitive membrane. If these changes are sudden, as for example in
our northern states where the temperature will vary from 50° to 70°
Fah., in a single day, the danger of injury becomes imminent, and the
lungs require to be strong indeed to resist their effects. Sudden
transition from the hot close atmosphere of the barn or stable to the
chilling winds of winter is equally hurtful. But it is not alone the
transition from warmth to cold that is injurious. The general relaxation
attendant on the sudden change from a cold bracing atmosphere to one
unduly hot is even more injurious. How frequently do human beings suffer
from colds as the result of a close sultry period at once supervening on
a clear cold one? How extensively do chest diseases prevail among horses
brought from the clear pure atmosphere of the field, and shut up in
close, hot stables? Here, no doubt, there is superadded the impurity of
the too often infected air, the change of diet, of exercise and of
general care yet we find that affections of the air passages are to a
great extent in ratio with the heat of the building. Hence their
constant presence in dealer’s stables where it is thought desirable to
keep the horses warm to hasten the improvement in the coat.
The suddenness of the transition is usually a principal cause of injury.
Where the climate changes slowly the animal economy becomes habituated
to it and resists successfully the injurious influences. Thus when
spring merges gradually into summer and autumn into winter, diseases of
this kind are far less frequent. But on the other hand a sudden and
extreme variation of temperature, whether in the ordinary course of the
season or from a wide change of latitude, is notoriously attended with
diseases of the air passages. Ayrshire, shorthorn and Jersey cattle,
when first imported into the Northern States of America, contract colds,
consumption and other chest diseases to a far greater extent than the
native races, though their progeny or even they themselves after
acclimatization, exhibit powers of resistance nearly equal to the native
stock. Sheep that have been shorn in midwinter or early spring often
repay the inhumanity of their owners by dying of inflamed lungs.
Southdown and Leicester sheep, sent from England to the north of
Scotland, demand at first the greatest care to protect them against the
increased rigor of the climate. The army veterinary statistics of France
show that horses transported from the southern parts of the country to
the more northern stations, suffer largely from pulmonary affections.
But if the change is effected slowly the requisite powers of resistance
are acquired and the novel conditions of life cease to be injurious.
That this varied power of resistance is not confined to the higher
animals would appear from the experiments of W. Edwards on cold blooded
animals. He subjected them in winter and in summer respectively to a
very low temperature and found that whereas in summer their temperature
declined 3° to 6° Cent., in winter they had a greater resistance and
barely declined ⁴⁄₁₀ths of a degree.
The action of cold on the surface of the body often leads to morbid
states of the air passages as the result of nervous sympathy. A beast is
subjected to a keen cold wind, is attacked with shivering, and
inflammation of the chest supervenes. The result is rendered more
certain if the wind is associated with rain and if the animal has been
previously in a state of perspiration. A heavy coat of hair, a profuse
perspiration, and a cold draught often combines effectively to produce
respiratory disease.
It must be added that the chilling debilitates the nuclei of the animal
tissues, and lessens their power of resistance to noxious influences.
The excess of cold in the freezing of a part, is followed by congestion
and even violent inflammation with perhaps sloughing after it has been
thawed. The persistence of such tissue debility is familiar to us all in
the example of chillblains. A less extreme application of cold affects
the tissues and nuclei less powerfully, but none the less surely. The
increased liability to disease of the chilled system is strikingly
illustrated in the experiment of Pasteur with anthrax. The chicken which
had proved refractory to an ordinary dose of anthrax virus, was dipped
in water at ordinary temperature until the heat of its body was reduced,
and then it fell an easy victim to the anthrax bacillus. In the same way
the person who recklessly exposes himself to wet and chill falls a ready
victim to intermittent or yellow fever from which he would otherwise
have escaped. Debility from another cause, such as bruise or laceration,
favors deep-seated invasion by pus cocci, and a resulting abscess, from
which the patient would have remained free, but for such traumatism.
But the effect of cold is not confined to the sympathy between the skin
and respiratory mucous membrane, nor the revulsion of the blood toward
internal organs, nor to the debilitating of the tissues. The application
of cold constringes the vessels and lessens the freedom of the
circulation and suppresses the normal cutaneous exhalation. A somewhat
similar condition may be induced by prolonged exposure to the rays of a
burning sun, the skin becomes hot, dry and rigid, and incompatible with
the maintenance of the respiratory function. In either case there is a
retention of effete and deleterious matters in the circulation which it
was the function of the skin to have eliminated. The danger of such
retention may be best exemplified by noting the result of the complete
repression of perspiration in the remarkable experiments of Fourcault
and Bouley. The former covered dogs and other small animals with an
impermeable varnish which induced death after some days or in some cases
in a few hours. Bouley shaved three horses and covered the skin with
tar. There resulted dullness, torpor, deep, slow breathing, weak and
diminishing pulse, muscular tremors, manifest cooling of the body and
expired air, and deep violet color of the mucous membranes. They died
respectively on the seventh, ninth and tenth days. A fourth horse
covered with a layer of strong glue and then with tar perished nine
hours after the application. The bodies were like those of animals that
had died of suffocation. The mucous membrane of the stomach and bowels
was gorged with black blood, the lungs violently congested—dark red and
heavy—the air tubes filled with frothy material, and the lining membrane
of the heart had dark spots of blood extravasation. It is no longer then
matter for surprise that temporary suppression of the insensible
perspiration should be followed by diseases of the chest or abdomen,
that extensive burns of the surface of the body should be speedily
followed by inflammations of internal organs or that extensive and
severe cutaneous inflammations should be associated with internal
lesions.
Since the days of Hippocrates it has been universally acknowledged that
moist seasons and localities are less salubrious than dry ones. As
already observed moisture in a cold atmosphere intensifies its effect.
In a hot, close atmosphere it strongly conduces to putrefaction in dead
organic matter, and the air becomes loaded as a consequence with noxious
gases, and in its lower strata with bacteria in a state of active
growth. This condition is most intense in close, unventilated stables,
and manifestly operates in both predisposing to and exciting those
diseases of the chest and other parts, so frequent in such places. Winds
raise and carry such germs, but also sooner rob them of virulence. (See
Zymotic Diseases). Susceptible, young animals, newly housed, usually
suffer the most severely from these injurious conditions. Often in their
case frequent, extreme and sudden changes, and great atmospheric
impurity, are combined with a diet to which they have been hitherto
altogether unaccustomed. In young horses there are superadded the
exertions—too often extreme—connected with training or work. There are
the heats and chills, the soaking perspiration and the frigid winds and
rain, the general exhaustion, but particularly the overwork of the
respiratory organs, each of itself calculated to superinduce disease.
Percivall justly remarks that among young horses, newly stabled and put
to work, the prevailing diseases are “catarrh, sore throat, strangles,
bronchitis, pneumonia and pleurisy.” His tables of the diseases
attacking the horses of his own regiment (1st Life Guards), are so
instructive that I here reproduce them:
A TABLE (COMPILED FROM EXTRACTS FROM A “REGISTER OF SICK HORSES”
LIMITED TO A GIVEN PERIOD) SHOWING THE COMPARATIVE AGES AT WHICH HORSES
APPEAR MOST DISPOSED TO CERTAIN ORGANIC DISEASES.
─────────────────┬────────┬────────┬────────┬────────┬────────┬────────
│ │ │ │ No. 10 │ │
│ │ │ No. │ Years │ │
│ │ │above 5 │ and │ │
│ No. of │ No. in │ Years │Upwards │ No. 20 │
│Patients│ Their │ and │ but │ Years │
│Under 5 │ 5th │ Under │ under │ and │
│ Years. │ Year. │ 10. │ 20. │Upwards.│ Total.
─────────────────┼────────┼────────┼────────┼────────┼────────┼────────
Disease of the │ │ │ │ │ │
lungs │ 170│ 50│ 20│ 50│ 10│ 300
Disease of the │ │ │ │ │ │
bowels │ 10│ 20│ 40│ 70│ 20│ 160
Disease of the │ │ │ │ │ │
brain │ 4│ 2│ 5│ 14│ 2│ 27
Disease of the │ │ │ │ │ │
eyes │ 30│ 10│ 70│ 35│ 5│ 150
─────────────────┴────────┴────────┴────────┴────────┴────────┴────────
It will be seen that nearly one-half of the sicknesses, occurring among
the horses of the regiment, were chest diseases, and that nearly
three-fourths of these were in animals under five years old, or in those
newly purchased from the country.
The subjoined table shows the relative prevalence of disease in
different months of the year, deduced from the Register above referred
to:
───────────────────────┬───────────┬───────────┬───────────┬───────────
│Disease of │Disease of │Disease of │Disease of
│the Lungs. │the Bowels.│the Brain. │ the Eyes.
───────────────────────┼───────────┼───────────┼───────────┼───────────
January │ 20│ 12│ 1│ 10
February │ 25│ 8│ ...│ 9
March │ 23│ 11│ 1│ 7
April │ 19│ 10│ 6│ 10
May │ 13│ 3│ 3│ 9
June │ 14│ 16│ 1│ 13
July │ 13│ 13│ 3│ 19
August │ 11│ 23│ 3│ 17
September │ 11│ 5│ 10│ 19
October │ 24│ 3│ 3│ 9
November │ 19│ 10│ 3│ 9
December │ 16│ 9│ 1│ 4
───────────────────────┼───────────┼───────────┼───────────┼───────────
Totals │ 208│ 123│ 35│ 135
───────────────────────┴───────────┴───────────┴───────────┴───────────
In this table the extraordinary prevalence of lung diseases in spring
and autumn is very noticeable. There only remains to notice the number
of deaths occurring in the same regiment from pulmonary and other
diseases.
Deaths from pulmonary disease 77
Deaths from other diseases (Glanders and Farcy and accidents 57
excepted)
It is thus seen that though individually less dangerous than many
affections of the abdomen, brain, etc., yet by reason of their greater
frequency chest diseases induce the greatest mortality among this class
of stock.
In treating of the diseases of this class of organs they will be
sub-divided according as they affect the _nose_, the _throat_, the
_neck_, and the _chest_.