Popular Science Monthly/Volume 3/August 1873/The Morbid Effects of Heat

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THE healthy human body has a temperature which varies but little either way from 99° Fahr. The heat required to maintain this temperature is derived from the oxidation within the body of the elements of the food. In other words, our bodies are furnaces; the food we take is the fuel which supplies the furnace, and the air we breathe is the draught that keeps the combustion going. The amount of heat thus evolved is, in health, always in excess of that needed to maintain the required temperature. There is, therefore, a constant overplus, a part of which is converted into mechanical work, while the remainder escapes as waste, partly along with the matters passing out of the body through the lungs, kidneys, and skin, and partly by the processes of conduction and radiation.

In estimating the morbid effects of external heat upon the living body, this waste requires to be taken into account, as its fluctuations, through the operation of surrounding conditions, have much to do with the regulation of the body-temperature. If, by exposure to cold, for example, heat is lost more rapidly from the surface than it is supplied within, its warmth must decrease, and there needs but a few degrees of fall to induce disease; on the other hand, if, by exposure to external heat, loss from the body is impeded, its temperature rises, and disease again results.

In hot climates, or during the hot season in temperate latitudes, we are in contact with an atmosphere which frequently attains a temperature nearly or quite equal to that of the body; and, at such times, our sensations tell us that we are losing heat less easily than during the cooler portions of the year. But, when thus exposed, the extensive evaporating surfaces of the lungs and skin are called into more active play; and, if the air is of average dryness, heat is rapidly thrown off by perspiration, the loss being so nicely adjusted that a uniform temperature of 99° Fahr. is continuously maintained. This heat-regulating function of the organism is one of the marvels of physiology. In spite of the vicissitudes of climate and season, it ever holds the temperature at a uniform degree, and, even under the stress of high artificial heat, is able to keep the balance comparatively unchanged. Blagden and Fordyce exposed themselves in an oven to a heat of 260° Fahr., without serious inconvenience, and with but a slight rise of temperature. But the air was dry, and the heat was kept down by perspiration. The substitution of moist for dry air in the oven hindered evaporation, and the temperature of the body rose rapidly. With this hasty sketch of the heat-producing and heat-regulating functions of the animal economy, we pass to a brief consideration of some of the more important ill-effects resulting from the action of excessive heat on the conditions of health and on the body itself.

High temperature is a powerful aid to decomposition. Dead organic matter, under its influence, speedily decays, giving rise to foul and poisonous products which, escaping into the atmosphere, find their way, sooner or later, into the system. Here they work various forms of mischief. Like sulphuretted hydrogen gas, they may be directly poisonous, or, like carbonic-acid gas, may act by diluting the air, and so, by reducing the normal supply of oxygen, interfere with the due oxygenation and purification of the blood. The filth of towns is always highly charged with organic matter, and this, when rapidly decomposing in the heats of summer, has long been recognized as a prolific source of disease.

Decaying vegetable matter in the soil is held to be the source of malarial poison; and here, again, if moisture is present, decay is always hastened and increased by excessive heat. So great, in the opinion of Dr. Parkes, is the influence of heat on the development and spread of malarious disease, that, in selecting a residence with a view to escaping its effects, he recommends that, in tropical countries, the point be 1,000 or 1,500 feet higher above the source of the poison than is required in temperate latitudes. The remittent form of malarious fevers, according to Dr. Maclean, "is most prevalent and fatal where high temperatures and malaria act in combination." The same authority also says: "I have, in a great many instances, observed intermittents pass at once into a severe type of the remittent form, apparently from no other cause than the descent from comparatively cool and elevated regions into the heated plains, and this under circumstances where there was no reason to believe that the sufferers had been again exposed to malaria."

In the production and spread of cholera, and yellow fever, excessive heat also has an important share. Both are most intimately associated with decomj)osing filth; both are conveyable by the putrefying stools of the sick, and both flourish most in hot climates and hot seasons. In the case of cholera, the bad effects of extreme heat are abundantly shown by what has been observed in the tropics. "In Bengal," says Dr. Goodeve (Reynolds's "System of Medicine," vol. i., p. 129), "the hot seasons, including the hot, and dry, and rainy seasons, have witnessed the worst epidemics." The most fatal cholera months, in both tropical and temperate countries, are found between April and September. Among European troops in Bombay, according to Dr. Ewart's tables, which cover a period of eight years, more than 50 per cent, of the cases treated in the six months from April to September died, while but little over 19 per cent, of the cases treated in the other six months of the year were fatal. That the disease occurs in winter is undoubted, but that it is much less general and severe is equally true. Yellow fever, though resembling cholera in many ways, is unlike it in this—a temperature of 70° or 72° Fahr. is absolutely requisite to its development and propagation, and the occurrence of frost at once puts an end to its ravages.

Heat also contributes largely toward the production of diarrhoea, its more common form, in recognition of this, taking the name of summer complaint. The disease is far more common and more fatal in hot than in cold climates, and in the summer season of temperate climates than in the winter. Putrefying organic matter, held in suspension in drinking-water, is, according to Dr. Parkes, one of the most common causes of diarrhoea, and this condition of the water is very frequent in summer, and comparatively rare in winter.

In all these instances heat appears to act not so much upon the body itself as upon the various external agencies influencing health. It is to bad conditions what fire is to powder. If the match is withheld, the powder is harmless; but, as the two are liable to come together, we secure safety by removing the magazine. So the presence of filth in water, in soil, and above-ground, may be innocuous by itself, but let the action of heat touch it off into decomposition, and we at once get the effects in the shape of disease. Heat thus aids the pollution of both air and water, keeps alive and active the germs of disease in the excreta of the sick, and in both ways favors the spread of contagion.

Its direct action upon the person becomes most apparent when some of the functions are going wrong. When the body is healthy, and proper precautions are taken in its management, there is little to fear from exposure to heat. Observers in tropical countries tell us that excessive heats are borne with impunity by the healthy, and that it is mostly those who are either temporarily or chronically out of order that eventually suffer. Not that the body can bear unlimited exposure to great heat, any more than it can endure continuous exertion, but that it is capable of maintaining itself under even excessive heat, if the exposure is not too prolonged. When its powers are impaired by some local or constitutional complaint, however, and it is less able to do the extra work which the influence of excessive heat imposes, then is the time when even slight exposure may be followed by the most serious consequences.

Authors describe several forms of acute disease that are traceable to heat as the exciting cause, but, as all of these partake more or less of the nature of sunstroke, and as we are writing for the public rather than the physician, it is not necessary here to go into their distinguishing features. Sunstroke, or the disease hitherto passing under that name, though known since early times, is even yet not well understood. Up to within a few years, it was believed by patient and physician alike that, to produce it, the body, and especially the head, must be exposed to the direct rays of the sun. There is now abundance of proof to the contrary. In his admirable little work, entitled "Thermic Fever, or Sunstroke," Dr. H. C. Wood quotes the records of its occurrence in barracks, hospitals, and tents, and not infrequently in the night-time, in many cases without immediate previous exposure to the sun. According to Dr. Bonnyman, as cited by Dr. Wood, "By far the greater number of cases that yearly occur in India are of men who have not been exposed to the sun. It is not unusual for men to go to bed in apparent health, and to be seized during the night; and patients in hospitals, who have been confined to bed for days previously, are frequently the subjects of attack." Dr. Swift testifies to its production by exposure to artificial heat, eleven cases treated by him having been attacked in the laundry of an hotel; while several others occurred in sugar-refineries. Dr. Wood mentions a case of his own, which also originated in a sugar-refinery. Dr. Maclean, in the second volume of Reynolds's "System of Medicine," quotes M. Boudin to the effect that one hundred cases of sunstroke occurred on the French man-of-war Duguesne at Rio Janeiro, most of them at night while the men were lying in their bunks. Much more of similar import might be offered, but enough has been said to show that it is great heat which precipitates the attack, and that it makes little difference whether this come from exposure to the direct rays of the sun, or from a highly-heated atmosphere, or indeed from some artificial source.

But while heat is rightly regarded as the principal if not the sole exciting cause, there are other conditions, as previously stated, which contribute largely toward bringing on the attack. Of these, overcrowding, and its associate, insufficient ventilation, are among the most important. The histories of the outbreaks that have occurred in barracks, in tents, and on shipboard, refer to these conditions as always present, and also mention that both officers and men in every other way similarly circumstanced, but provided with plenty of room and ventilation, did not suffer.

Another and equally important predisposing cause is the exhaustion produced by prolonged exertion. The fact that a large proportion of the cases occurring in this country are of persons engaged in laborious occupations is evidence of this, and if more is needed it is found in the experience of army-surgeons in India, who state that some of the severest epidemics ever witnessed in that country took place among the troops toward the close of long and fatiguing marches, when not a case was observed while the men were fresh and vigorous.

Want of acclimatization is set down as another powerful predisposing cause. "Foreigners," says Dr. Wood, "are always attacked in much larger numbers than natives of the tropics. It must be remembered, however, that no amount of acclimatization will afford certain protection, as even the Hindoo, born and bred in the stifling air of Bengal, is occasionally attacked.

Tight-fitting clothing, which impedes the circulation and hinders the movements of the body, likewise invites attack. Formerly soldiers in India were dressed, in the hottest weather, with tightly-buttoned coats, stiff leather stocks, heavy cross-belts over the chest, and a cap peculiarly adapted to concentrate the rays of the sun upon the head. When so accoutred, according to the testimony of their medical officers, sunstroke among them was common; and, since this style of dress has been done away with, it is much less frequent.

Persons addicted to spirit-drinking are by many writers believed to furnish a much larger proportion of cases than abstainers.

The presence of a large amount of watery vapor in the air is held, by Parkes and others, to predispose to sunstroke. By opposing evaporation from the surface, it favors the rise of animal temperature.

Other causes predisposing to sunstroke are given by different writers; they are, however, of the same general nature as those already enumerated, being simply conditions which either diminish the powers of the system, or for the time being impose upon them some heavy tax. Whether death from sunstroke is due to the action of heat on the nervous system, or to the coagulation of the muscle-plasma (myosin) of the heart, or to blood-poisoning, or in some cases to one, and in others to another of these causes, as maintained by different physicians, it is not necessary here to inquire. What chiefly concerns us now, having pointed out the principal causes of the disease, is to learn something of its symptoms, how in the absence of the doctor it should be treated, and what to do to avoid it.

The serious disturbance of all the functions occasioned by sunstroke results, as might be expected, in a great variety of symptoms. In a small proportion of cases, however, the attack is so sudden and so quickly fatal that little chance for the development or observance of symptoms is afforded. The patient suddenly falls, gasps a few times, and dies. But, in the majority of instances, premonitory symptoms are present. The more constant, as given by the best authorities, are great heat and dryness of skin, a varying degree of pain in the head, attended oftentimes with giddiness, congestion of the eyes, full, rapid pulse, which grows feeble and irregular as the disease advances, obstinate constipation, irritability of bladder, and great oppression or sense of weight about the region of the heart, with not unfrequently muscular weakness and a disinclination for exertion. If these symptoms continue, the patient soon passes into a state of profound insensibility. The pupils fail to respond to the action of light, and may be somewhat contracted, the breathing becomes hurried and difficult, and the action of the heart is irregular and tumultuous. Convulsions may come on early, or be postponed until late in the disease, or they may be absent altogether. Numerous minor and less constant phenomena have been recorded by different observers; but, when a person is suddenly attacked during exposure to great heat, the symptoms already enumerated will enable any one of ordinary intelligence to recognize the true character of the disease.

Only such measures of treatment will be suggested as any one of common-sense can apply; and they may be the means, if promptly resorted to, of ultimately restoring the patient, when, if nothing were done until the physician arrived, he might then have passed beyond the reach of help.

When the signs of an attack appear, the sufferer should be immediately taken to the nearest shade, preferably in the open air, but, at all events, where the freest ventilation can be secured. His body should at once be stripped, and the head, neck, and chest, continuously drenched with cold water. Let this be followed up, not timidly, but with boldness, until respiration is reestablished, after which it may be applied at short intervals, until a perceptible diminution of the temperature of the body has taken place, or until the doctor arrives. It is the great heat of the body that menaces life, and, the sooner this can be reduced into the neighborhood of the natural temperature, the better for the patient. In rare instances this free use of cold water, by the powerful impression it makes on the nervous system, excites convulsions, in which case it may be discontinued, and rubbing the surface with pounded ice resorted to. An injection of ice-cold water,

as recommended by Dr. Parkes, may, at the same time, be given. When he can swallow, the patient should be encouraged to drink freely, and, if vomiting follows, so much the better, as this tends to relieve the lungs, which are always greatly congested. Other measures of treatment, and the management of after-consequences, may be most safely left in the hands of the physician.

After what has been said, the means to be adopted for the avoidance of sunstroke will readily suggest themselves. Great care must be taken to preserve intact the function of the skin, and nothing is better for this than frequent bathing, and friction of the surface. Hard labor, in a close, highly-heated atmosphere, or during extreme hot weather, in the sun, should be carefully shunned, and the use of spirits, if previously indulged in, entirely discontinued. The dress should be such as will permit free loss of heat, preferably linen, and on no account should it be so close fitting as to hinder the motions of the chest, neck, or head. A light hat, permitting free circulation of air about the top of the head, is very useful. English troops in India wear light wicker-helmets made of bamboo, and covered with cotton. These permit thorough ventilation of the head, and, according to Dr. Parkes, have diminished the frequency of sunstroke.