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.