_Causes._ These are not well understood. Low, damp situations would seem
most liable, especially if the animals are much exposed at night. So far
indeed as can be observed it arises from the same causes as
_laryngitis_. Age affects its development. Croup is mostly seen in
animals between six months and a year old, and rarely in those over five
or six years of age. The specific cause of the formation of false
membranes and of spasms of the laryngeal muscles is a mystery, but to
these the susceptible constitution and tissues of young animals appear
to predispose. No mere grade of inflammation from the slightest
hyperæmia to the highest type of inflammatory action is of itself
sufficient to arouse the special phenomena. All of these are seen
everywhere but _croup_ may be said to be confined to certain localities
and ages.
_Symptoms._ Unless it supervenes on a pre-existant attack of catarrh,
croup is usually as sudden in its outset in the lower animals as in man.
An extremely hard _croupy_ cough, or loud, crowing, difficult breathing,
loudest in inspiration, is usually the first symptom and appears to
seize the animal in an instant and without the slightest premonition.
This is closely followed by intense fever, full, hard pulse, 80 to 100
and upward per minute, increase of bodily temperature sometimes to
107.5° F., costiveness and high colored scanty urine. The throat is
excessively tender, the slightest touch giving rise to violent paroxysms
of coughing, during which the eyes redden and protrude from their
sockets, the veins of the skin are gorged, the tongue, dry and livid, is
protruded and small portions of the contents of the stomach and white
shreds of false membrane are occasionally brought up. Sometimes in the
intervals of coughing as well the mouth is constantly open and the
tongue protruded and partly covered by a frothy but tenacious mucus.
Suffocation appears imminent in many cases and the beast may perish
suddenly in this way. On the other hand the threatening symptoms may be
present only at certain periods of the day and may be moderated
remarkably at others, especially at early morning. If complicated by any
chest affection the symptoms are more urgent and the issue more commonly
fatal. If associated with a low type of fever, a small, weak pulse, and
much prostration, as it tends to be if it continues several days without
relief, it has a more fatal tendency. The same may be said of its
occurrence epizootically.
_Duration._ Croup will often run its course and prove fatal in
twenty-four to forty-eight hours. Improvement is manifested by the cough
becoming less convulsive and painful, by the expulsion through the mouth
of shreds of false membrane, and by return of spirits and appetite.
_Postmortem Appearances._ If the animal has died suffocated, the lungs
and right side of the heart will be gorged with blood; if in a stupor
(coma), attendant on brain poisoning with venous blood, the veins will
be specially engorged. The mucous membrane of the larynx has a more
vivid arborescent redness than in ordinary laryngitis but the special
feature is the presence of false membranes. These layers of exuded
material are almost confined to the air passages. They may extend to the
soft palate and nose in an upward direction and to the trachea and
bronchial tubes in a downward, but they rarely exist in the mouth,
pharnyx, or gullet like the false membranes of diphtheria.
_Characters of the false membranes._ These are gray or yellowish white,
though they may be reddened in patches or streaks. They vary in
consistency from that of glairy mucus to a firm layer as of dense
fibrine, and become more adherent as they are of older standing.
Sometimes they are partially detached, the free end of the shreds
floating in the larynx. The deep or attached surface presents redness in
points, in streaks, or as ramifications very visible if the membrane is
held up between the eye and the light. They vary in thickness from half
to a line. Delafond has found these membranes in the lower animals to be
mostly formed of fibrine, with a little albumen, and traces of alkaline
and earthy salts.
_Treatment._ This must be prompt and energetic. Wet cloths as hot as the
hands can bear, wrapped around the throat and neck, and replaced as they
cool, will usually arrest the spasm. If this fails ether or chloroform
by inhalation or chloral hydrate by injection may be employed with
caution. The action of the bowels must be secured by salines (sulphate
of soda ½ to 1 ℔) or oil (linseed oil ½ to 1 pint) and injections of
warm water. Sulphate of soda should be thereafter given in half ounce
doses twice daily, or nitrate or acetate of potass may be substituted.
They are advantageously given in linseed decoction and may be combined
with laudanum, (½ ounce), belladonna, or other agent to check the
spasms.
A blister (mustard poultice) should be applied at first either to the
throat or breast, the windpipe being left untouched lest tracheotomy
should be required. Similar applications to the legs are useful.
If suffocation appears imminent _tracheotomy_ should be at once
performed (see under Laryngitis). This operation has been depreciated
because of the late period at which it has been employed, when the
patient was already past all hope, but the resulting wound in the neck
is more than counterbalanced by the greater freedom of breathing and the
better æration of the blood which tends to obviate the justly dreaded
low fever. It often leads to a rapid diminution of the spasms and
laryngeal irritation.
Agents applied directly to the inflamed mucous membrane are often
requisite. The air of the building should be rather warm, equable and
moistened by water vapor, if that can be conveniently done. Calomel or
alum powder may be frequently introduced into the larynx by means of a
whalebone prob and sponge as spoken of under laryngitis, or a solution
of nitrate of silver (10 grains to the ounce of water) may be applied
several times a day. These not only hasten the removal of false
membranes but counteract their production. They produce violent and
convulsive coughing at first and have to be used carefully. Delafond
blew in such agents through an opening made in the windpipe. They may be
injected with a hypodermic syringe. In prostrate conditions it may be
necessary to resort to stimulants (wine whey, carbonate of ammonia) and
tonics (gentian, Peruvian bark).