Definition: two forms. =Heat exhaustion.= Causes: prolonged heat, and
moisture, overexertion. Impaired vaso-motor centre. Failing heart.
Carbon dioxide poisoning. Symptoms: weak, fluttering pulse,
perspiration, muscles flaccid, prostration, no hyperthermia.
Treatment: stimulant, digitalis, digitalin, subcutem, nitro-glycerine,
warm baths. =Thermic fever.= Hyperthermia excessive. Causes:
insolation, prolonged heat and impure air, furnace heat, moist and dry
heat, electric tension, overwork, muscular exhaustion, coagulation of
myosin, constant heat on one part (head), excess of carbon dioxide,
stiffening of bodies when killed in hot weather, debility, weakness,
fatigue, chest constriction, tight girths or collars, short bearing
reins, plethora, obesity, open cars and yards, fever, privation of
water, heavy fleece. Lesions: right heart and systemic veins full,
blood black fluid or diffluent, left ventricle empty, congested
meninges, effusions in or on brain, or hæmorrhages. Symptoms: =horse=:
dull, stupid, stubs toes, sways quarters, droops head, hangs on bit,
props on feet, breathes rapidly, pants, stertor, dilated nostrils,
gasping, fixed eyes, dilated pupils, tumultuous heartbeats, gorged
veins, epistaxis, perspiration, convulsions: =ox=: parallel symptoms:
=sheep=: open mouth, stertor, fixed eyes, pupils dilated, panting,
swaying, fall, convulsions: =dog=: dull, prostrate, pants, congested
veins and mucosæ, weakness, spasms, syncope, speedy rigor mortis.
Overheating. Diagnosis: early excessive hyperthermia, venous
congestion, shallow panting breathing, violent heart action, loss of
sensory and motor functions, convulsions. Prevention: avoid violent,
prolonged heat, and exertion, especially in case of fat animals or
those new to hot climate, keep emunctories acting, shade head, water
on head and to drink, protect fat cattle, shear sheep, water.
Treatment: shade and laxatives; if severe, cold water from hose, ice
bags to poll, rub legs, acetanilid subcutem, stimulant enemata, later
mineral tonics, iron or zinc.
_Definition._ A morbid condition produced by the exposure to extreme
heat, and marked by profound disorder of the _vaso-motor_ and _heat_
centres.
The single term of _sun-stroke_ or _heat-stroke_ has been replaced by
two,—=heat exhaustion= and =sun-stroke=, indicating two distinct
conditions, brought about by exposure to heat and manifested by
different states of the body and distinctive symptoms.
Heat Exhaustion.
This appears as an exaggerated form of the general sense of relaxation,
weakness and languor which follows on prolonged violent exertion in a
hot atmosphere. There is more or less impairment of the vaso-motor nerve
centre in the medulla, relaxation of the capillary system, and flagging
of the heart’s action, which loses its customary stimulus, by reason of
the defective supply of blood returned by the veins. This may become so
extreme that the patient dies by syncope. In other cases the paresis is
mainly shown in the vaso-motor system, and its centres in the medulla,
the blood is delayed in the distended capillaries and veins, it becomes
overcharged with carbon dioxide, the heart’s action is accelerated and
feeble, the pulse rapid, weak and fluttering, perspiration breaks out on
the skin, and the temperature is normal or subnormal. The muscular
weakness, the flaccid condition of the facial muscles, and general
depression suggest a state of collapse. This condition is not
necessarily due to exposure to the intensity of the sun’s rays, but may
come on in animals subjected for a length of time to artificial heat,
and especially if the air is impure, and if the subject has to undergo
severe physical exertion.
_Treatment._ In slight cases of this kind a stimulant is usually
desirable and ammonium carbonate in bolus or solution will usually serve
a good purpose. In its absence alcohol or spirits of nitrous ether may
be given. Digitalis is of great value in sustaining the flagging action
of the heart and has the advantage that as digitalin it can be given
hypodermically when it is impossible to give ammonia, alcohol or ether
by the mouth. For the same reason nitro-glycerine may be resorted to, or
even atropia as a vaso-motor stimulant. Active friction of the body and
limbs will aid circulation and indirectly stimulate the heart, and in
case of subnormal temperature it may be supplemented by a warm bath in
the smaller animals, kept up until the normal temperature in the rectum
has been restored.
Thermic Fever. Sun-stroke.
This is readily distinguished from _heat exhaustion_ by the predominance
of the hyperthermia. While in =heat exhaustion= the temperature is
usually subnormal, in =sun-stroke= it is excessive, (108°–113° F.).
_Causes._ The immediate cause of sun-stroke is exposure to undue heat,
but this need not be the heat of the sun’s rays direct. A large
proportion of cases in the human subject are attacked during the night,
and again at sea where an attack in a passenger is practically unknown,
it is terribly common among stokers working in a close atmosphere of
100° to 150° F.
The attendant conditions have much influence in determining an attack,
thus it is generally held that heat with excess of moisture is the most
injurious, yet in Cincinnati, statistics showed a greater number of
cases in man when the air was dry. The suppression of perspiration and
the arrest of cooling by evaporation in the latter case would tend to a
rapid increase of the body temperature, and the condition would be
aggravated by the electric tension usually present with the dry air.
With the hot, moist air perspiration might continue, but evaporation
would be hindered, and there would be arrest of the cooling process and
an extreme relaxation of the system.
Again, if is usually found that seizures take place during or after hard
muscular exertion in a hot period, and much importance is attached to
the attendant exhaustion, the excess of muscular waste, and the
alteration of the myosin, which latter coagulates at a lower temperature
in the overworked animal. But on the other hand, experiment shows that
the animal confined to absolute inactivity in the hot sunshine or in a
high temperature (at 90°), dies in a few hours, whereas another animal
left at liberty in the same temperature does not suffer materially. The
explanation appears to be that the dog, kept absolutely still, has the
continuous action of the heat on the same parts and on the same blood,
for the capillaries dilate, and the blood is delayed, overheated, and
surcharged with carbon dioxide, and the result is either syncope from
heart failure, or asphyxia from excessive carbonization of the blood.
Back of these and concurring with them is the paralysis of the
vaso-motor and heat generating nerve centres, from the high temperature
or the condition of the blood.
The excessive carbonization of the blood deserves another word. The
prolonged contact of the blood and air in the lungs is essential to the
free interchange of oxygen and carbon dioxide. Vierordt showed that with
sixty respirations per minute the expired air became charged with but
2.4 per cent. of this gas, whereas with fourteen respirations it
contained 4.34 per cent. Therefore, with violent muscular work (which
charges the blood with carbon dioxide) and rapid breathing (which fails
to secure its elimination), the overdriven animal soon perishes from
asphyxia. Under a high temperature of the external air, this condition
is aggravated since the rarefied air contains just so much the less
oxygen, the absorption of which is the measure of the exhalation of
carbon dioxide.
Dr. H. C. Wood, who has experimented largely on the subject in animals,
finds the cause of heart failure in the coagulation of the myosin, which
takes place under ordinary circumstances at 115° F., but at a much lower
temperature when a muscle has been in great activity immediately before
death. As the temperature of thermic fever frequently reaches 113°, or
even higher, he easily accounts for the sudden syncope occurring during
active work in a high temperature. As an example of such sudden rigor,
he adduces the sudden stiffening of the bodies of some soldiers killed
in battle during hot weather.
Wood further shows that all the symptoms of thermic fever can be
produced in the rabbit by concentrating the temperature on its head,
which seems to imply a direct action on the brain and in particular on
the heat producing and vaso-motor centres. This becomes the more
reasonable that the temperature attained does not impair the vitality of
the blood but, leaves the leucocytes possessed of their amœboid motion.
He found, moreover, that if the heat were withdrawn before it has
produced permanent injury to the nervous system, blood or other tissues,
the convulsions and unconsciousness are immediately relieved and the
animal recovers.
Other conditions may be adduced as predisposing or concurrent causes of
thermic fever. Whatever impairs the animal vigor has this effect.
Fatigue, as already noticed, is a potent factor, in man a drinking
habit; in all animals a long persistence of the heat during the night as
well as the day; impure air in badly ventilated buildings; and
mechanical restriction on the freedom of breathing. In military barracks
with the daily temperature at 118° F. and the night temperature 105, the
mortality became extreme, and in close city car stables the proportion
of sun-strokes is enhanced. In all such cases, the air becomes
necessarily more and more impure continually. The atmosphere has the
same heat as the animal body, so that no upward current from the latter
can be established, to create a diffusion. The carbon dioxide and other
emanations from the lungs, the exhalations from the skin, dung and
urine, accumulate in the air immediately surrounding the animal and
respiration becomes increasingly imperfect and difficult. This condition
is further aggravated by the accumulation of the animal heat in the
body. The blood circulating in the skin can no longer be cooled, to
return with refrigerating effect on the interior of the body, the
cooling that would come from the evaporation of sweat is obviated by the
suppression of that secretion, as well as by the saturation of the zone
of air immediately surrounding the body, and thus the tendency is to a
steady increase of the body temperature until the limit of viability has
been passed.
The mechanical restriction of respiration should not be overlooked. In
European soldiers landed in India and marched in the tight woolen
clothing and close stocks a high mortality has been induced and in
horses with tight girths or collars and short bearing reins, and oxen
working in collars a similar result is observed. Any condition of fever
is a potent predisposing factor.
Horses or cattle that are put to violent or continued exertion when too
fat or out of condition are especially subject to sun-stroke. Fat cattle
driven to market under a hot sun, or shipped by rail, crowded in a car
and delayed on a siding under a hot sun, with no circulation of air,
often have insolation in its most violent form. The same may be seen in
the hot stockyard, with a still atmosphere and the fat animals subjected
to the full blaze of a July sun. The chafed feet caused by travel, and
the muscular weariness caused by standing in the moving car are material
additions to the danger.
Similarly horses suffer on the race track when subjected to protracted
and severe work in hot weather, or again dragging loads in a heated
street under a vertical sun, or on a side hill with the sun’s rays
striking perpendicularly to its surface.
A change in latitude has a decided effect, the Northern horse suffering
much more frequently than the one which is native to the Southern States
and which has inherited the habit of heat endurance.
Finally faults in feeding and above all watering are appreciable
factors. The privation of water in particular is to be dreaded. Tracy in
his experience with American soldiers in Arizona, found that the command
could usually be guarded against sun-stroke when a supply of water was
kept on hand. It should be used guardedly, but nothing would act better
in obviating an attack. On the other hand, when the canteens were empty,
under the hot sun the seizures increased disastrously.
Sheep are especially liable to suffer from heat by reason of their dense
fleece, which hinders the evaporation of perspiration, and the cooling
effect of air on the skin. When the temperature rises, respiration is
accelerated and panting, the lungs seeking to supplement the work of the
skin. When traveling in a heavy fleece, or in the hot sunshine in July
or August sun-stroke is not uncommon among them.
_Lesions._ Among the lesions may be named, vacuity of the left ventricle
and fullness of the right ventricle and veins with fluid blood or a
diffluent clot; congestion of the pia or dura mater, effusion into the
ventricles, hæmorrhages into the subserous tissues, and degeneration of
the muscles.
_Symptoms._ =Horse.= When premonitory symptoms are observed the animal
fails to respond to whip or voice, lessens his pace, stubs with his fore
feet and sways with the hind, depresses his head and hangs heavily on
the bit.
Too often these are omitted or overlooked, and the horse suddenly stops,
props himself on his four limbs, drops and extends the head, breathes
with great rapidity, panting and even stertor, dilates the nostrils
widely, retracts the angle of the mouth and even gapes, has the eyes
fixed, the pupils dilated and the beats of the heart tumultuous. The
superficial veins are distended, the visible mucosæ congested with dark
blood, and blood may escape from the nose. Perspiration usually sets in.
The animal may fall and die in a few minutes in convulsions, or, if
stopped sufficiently early and suitably treated, he may in a measure
recover in 15 to 20 minutes.
_Symptoms._ =Ox.= The premonitory symptoms are like those in the horse:
dullness, rapid, panting breathing, the mouth is opened and the pendent
tongue is covered with frothy saliva, a frothy mucus escapes from the
nose, the eyes are congested and fixed, the pupils dilated, the nostrils
and flanks work laboriously, the heart palpitates, the animal sways or
staggers and falls. Death follows in convulsions, or it may be delayed,
the animal struggling ineffectually to rise, or having periods of
comparative quiet. The rectal temperature is very high, 107° to 114° F.
If able to stand, there is usually blindness and heedlessness of
surrounding objects.
_Symptoms._ =Sheep.= The open mouth, protruding tongue, frothy saliva,
reddened fixed eyes, rapid breathing, beating flanks, stertor, and
unsteady gait are characteristic when taken along with the manifest
causes. Swaying movements followed by a sudden fall and death in
convulsions form the usual termination of the disease.
_Symptoms._ =Dog.= These have been mainly produced experimentally and
consisted in hyperthermia, dullness, prostration, accelerated breathing
and heart action, congested veins, and mucosæ, muscular weakness,
convulsions, and syncope or asphyxia. After death the muscles became
speedily rigid, and the blood accummulated in the venous system, was
fluid or only loosely coagulated. In these animals, if the experiment
were stopped in time the animal could be restored to health.
Slighter cases may occur in the different animals, more particularly
from overdriving in hot weather, and in such cases the _overheated_
animal recovers, but there is liable to remain a special sensitiveness
to excessive heat and a tendency to be dull, sluggish and short winded,
to hang the head in hot weather, and to seek shelter from the direct
rays of the sun.
_Diagnosis_ is largely based on the suddenness of the attack, on the
occurrence of high temperature before the seizure, not after as it is
liable to be, if at all, in apoplexy, on the dark congestion of the
mucosæ, and of the venous system, on the rapidity and shallowness of the
respirations, on the tumultuous action of the heart, and on the general
loss of sensory and especially of motor function, in circumstances
calculated to induce sun-stroke. Localized paralysis or spasm would
suggest the formation of a cerebral effusion or clot.
_Prevention._ This will depend on the class of animal and its conditions
of life and work. In horses care should be taken to regulate the work by
the heat of the season and condition of the animal. When the temperature
ranges from 80° to 100° F. the work should be lessened and every
attention should be given to maintain the healthy functions (bowels,
kidneys, skin) in good working condition. If the horse is young, fat, or
out of condition from idleness or accumulation of fat he must have the
greater consideration. So it is with a horse recently come from a colder
latitude, and with a heavy draught horse that may be called on to do
rapid work. Some protection is secured by wearing a sunshade or a wet
sponge over the poll, and much may be expected from an occasional rest
in the shade, a swallow of cool water and sponging of the head.
Very heavy fat cattle should not be driven far nor shipped on the
hottest days, and the packed car should not be left in the full sunshine
in a still atmosphere. Yards with sheds under which they can retreat
must be secured if possible.
The heavily fleeced sheep must have equal care and the pastures for fat
sheep and cattle should have available shade in form of trees, walls or
sheds. Access to water is an important condition.
_Treatment._ In slight cases (_overheated_) a few days of rest, under an
awning rather than in a close stable, with a restricted and laxative
diet.
In severe thermic fever the first consideration is to lower temperature.
If available turn a hose on the head, neck and entire body for five or
ten minutes, or until the rectal temperature approaches the normal. In
the absence of such a water supply, dash cold water from a well on the
body but especially the head and neck, and if available tie a bag of ice
around the poll. Active friction to the legs and body is often of great
advantage. A large dose of antipyrin or acetanilid may be given
hypodermically. On the other hand stimulants, and especially carbonate
of ammonia, or sweet spirits of nitre may be given as an enema. This may
be repeated in an hour in case the pulse fails to acquire force and
tone.
Should the temperature rise again later it may often be kept in check by
cold sponging and scraping followed by rubbing till dry.
In case of continued elevation of temperature, with heat of the head,
and perversion of sensory or motor functions, meningitis may be
suspected and appropriate treatment adopted.
For the prostration and weakness that is liable to follow thermic fever,
mineral tonics such as the salts of iron or zinc may be resorted to.