Definition. Differentiation from acute vascular congestion.
Predisposing causes, age, sex, stabling, training, diet, impure air,
low health, previous lung disease, plethora, climate, season, exciting
causes, chill, fatigue, leucomaines, sudor, draughts, plunging in or
spraying with cold water, clipping, inhalation of irritant smoke, gas,
dust, drawing of food, irritating or insoluble drugs into the lungs,
neoplasms, parasites, contusions, fractured ribs, punctures,
contagion, plurality of germs, bacillus of Friedländer, micrococcus of
Talamon and Fränkel, diplococcus pneumoniæ equina of Schütz,
diplococcus pneumoniæ equina of Cadeac. Symptoms, chill, hyperthermia,
dullness on percussion and crepitation in the lower part of the lung,
reaction, congested mucosæ, accelerated labored breathing, excited
circulation, pulse oppressed, cough deep, patient statant, elbows
everted, nose protruded, nostrils dilated, approaching door or window,
pinched countenance, skin dry, harsh, adherent, partial sweats, loins
insensible, nasal discharge rusty, dependent part of lung largely
non-resonant, with peripheral crepitation. Blowing in abnormal
situation over hepatized lung. Decubitus, its significance. Course.
Results. Favorable indications in pulse, breathing, face, temperature,
appetite, decubitus, clearing of lung. Unfavorable indications in
breathing, pulse, fever, face, uneasy movements, pawing, cold limbs,
prostration, nervousness, weakness. Sabacuto Pneumonia. Terminations
of pneumonia, death, resolution, splenisation, abscess, gangrene, red
hepatisation, gray hepatisation, fibrinous consolidation. Lesions.
Congestion, exudation and cell growth, hepatization—red and gray,
deliquescence, abscess. Blood, loss of red globules, increase of
white, excess of fibrine, glandular swelling, pleurisy, degenerations
in other organs, laminitis, rheumatism. Treatment, adapted to strength
of subject and type of disease, hygienic, anti-rigor, antiphlogistic,
expectant, stimulant, antipyretic, febrifuge, sedative, moist
compresses, derivatives, laxatives. In subacute form tonics, heart
stimulants, febrifuge. In chronic cases add rich digestible diet, and
easy open air life.
This consists in inflammation of the spongy tissue of the lung involving
mainly and primarily the walls of the alveoli and interlobular
connective tissue with their respective trophic centres (nuclei). The
acute congestion of excessive heart action and debilitated pulmonary
capillaries described above, is primarily a disease of the bloodvessels
which become over distended and may or may not lead to the inflammatory
processes in their walls and the tissues adjacent. Pneumonia on the
other hand is essentially inflammation of these tissues and nuclei, with
exudation usually of a fibrinous material into their substance.
PREDISPOSING CAUSES. =1.= =Age.= A very early age is nearly exempt, and
from 6 years upward there are fewer cases relative to the equine
population, variations that may be better accounted for by stabling,
training and acquired immunity than by the mere fact of age. Of 237
cases, 2 were 3½ years; 32 were 4 years; 19 were 5 years; 131 were 6 to
11 years; 46 were over 11 years; and 7 of uncertain age (Trasbot). =2.=
=Sex.= No visible effect. =3.= =Stabling, training, change of food.=
While the young colt at pasture is practically immune, the period of
stabling, transition to a dry and grain diet, and to the nervous
excitement attendant on training and unwonted work as shown in the
statistics of Percivall and Trasbot determine an enormous increase of
cases. In a cavalry regiment Percivall found that 56.6 per cent. of all
lung diseases occurred before the 5th year, and Trasbot found that at
the Alfort Veterinary College 13.5 per cent. of all equine pneumonias
occurred in the 4th year. =4.= =Hot Stables.= =Impure Air.= These two
conditions usually coexist and prove potent causes especially in young
horses brought from the fields. We cannot, however, separate this cause
as usually observed from the action of pathogenic germs which are
preserved and concentrated in such places. =5.= =Poor Health.=
Debilitating diseases, insufficient and poor diet, overwork, exposure to
cold draughts or darkness and any other cause which lowers the vitality
predisposes. =6.= =A Previous Attack.= This usually leaves some
structural or functional change which renders the lung more susceptible
to a subsequent invasion. Against this must be placed the immunity which
follows the contagious forms, but as this is usually exhausted in the
course of six months it does not invalidate the position that the
permanent impairment of pulmonary integrity is a predisposing cause.
=7.= =Plethora.= Tending as this does to congestion it must be accepted
also for the next pathological step—pneumonia. =8.= =Climate and
Season.= This is notoriously an important factor. At Paris, Trasbot met
with 237 cases in the nine months from October to June inclusive and but
8 cases in the summer months—July, August and September. In Great
Britain, where the vicissitudes are less severe Percivall had in the
cavalry horses in the seven months from October to April inclusive 146
cases = 20.85 Per month, and in the 5 months from May to September
inclusive 62 cases = 12.4 per month.
_Exciting Causes._ Nearly all the above causes when acting with unusual
force may become direct factors in causation. The effect of a sudden and
extreme chill is especially to be feared. Even in cases that are
unquestionably due to a microbe as the essential cause, the nervous
disorder manifested in the chill, and the clogging of the pulmonary
circulation in connection with the retrocession of blood from the
surface of the body furnishes the opportunity for the colonization of
the germ. The average horse at pasture will stand with impunity cold
storms of rain, snow, and sleet, and transitions from a warm noonday sun
to a cold night wind and dew and even frost, but under other conditions
of the system, with the fatigue and fret and sudden changes of food and
regimen attendant on domestication, or with any derangement of an
important bodily function the _chill_ is often the manifest occasion of
disturbance of the balance of health, and the supervention of pneumonia.
=Fatigue=, a system charged with =leucomanies=, and a =free
perspiration=, which is suddenly checked by exposure, at rest, to a
=cold rain=, or =snow=, to a =draught between door and window=, to
=immersion in the cold waters= of a river, or to =sponging with cold
water= is quite liable to cause pneumonia. An unduly heavy winter coat,
an individual peculiarity or determined by a cold environment in autumn
often predisposes strongly to such dangerous chills, by the frequency
and profuseness of the perspirations and general relaxation of the
system. Clipping of such subjects is a true hygienic measure though it
entails the need of extra care in blanketing. Again in the animal that
has already suffered from disease of the respiratory organs these chills
are more dangerous factors.
=Direct irritation= by inhalation of smoke and other products of
combustion; or acrid or irritant gases or dust; by the drawing of food
by aspiration into the lungs (as in paralysis of the larnyx or pharnyx,
choking, apoplexy, vomiting, etc.); by pouring irritant or insoluble
drugs (oil, lard) through the nose; by the pressure of neoplasms
(actinomycosis, tubercle, glanders, cancer); or by the presence of
parasites (strongylus, distomata, echinococci, linguatulas).
_Pneumonia_ from =Contusion= of the chest, fracture of a rib, or
puncture or laceration of the lung is recognized.
=Contagion.= The presence of a _contagium_ in pneumonia is today well
established. Clinical observation had indicated this even before the
discovery of a specific germ, but recent bacteriological investigations
and the transmission of the disease by inoculation of artificial
cultures have definitely settled the question. It does not follow that
all cases are contagious, nor equally so, but the recognition of the
contagious form satisfactorily explains the prevalence of the disease in
one stable while an adjoining one escapes, and the eruption of new cases
in a stable after an animal affected with the disease or convalescent
from it has been introduced. It has been objected that many horses stand
in the stable with pneumonia cases and escape, but so is it with
glanders, cowpox, and many other affections. It merely argues an
immunity in the case of some, and for the disease germ a very limited
transmissibility through the air. The further objection that the
existence of lesions in the lung before the onset of fever, excludes
this from the list of infectious diseases, is untenable since many
undeniably contagious diseases, like cutaneous anthrax, glanders, lung
plague, cowpox, appear locally before any constitutional disturbance
occurs, which later as the result of extensive local disease and the
circulation of toxins in the blood. It places contagious pneumonia
however in that long list of infectious diseases which develop first
locally in the seat of infection and later become more or less
generalized.
It must be admitted however that the germ of pneumonia is not the same
for all cases of the disease and for all genera of animals. It must also
be allowed that the same germ does not always maintain the same degree
of virulence, and that it may even live for a time on the buccal mucosa
of an animal belonging to a susceptible genus without any morbid result.
In short we must recognize that different germs of pneumonia may become
temporarily non-virulent or only slightly virulent, and remain
pathologically quiescent, as for example during the summer months, to
reassert itself later when the conditions become more favorable to its
pathogenesis.