8 Boston Med. and Surg. Journ., June, 1864, p. 349.
About 1869, Eulenberg and Vohl9 advanced the theory that death from sunstroke is the result of the sudden liberation of gases in the blood; and Weikard affirmed that the death is due to the increase of the coagulability of the blood and consequent formation of clots in the vessels, being in this supported by Richardson of London.10 Contrasting with these in its being really an important contribution is the article of Vallin:11 its chief merit is the conception of the idea of the local heating of isolated parts of the body, and the devising of a plan for carrying the idea into effect. The experiments of Vallin did not themselves prove very much, and led him to the erroneous conclusion, first, that the death in sunstroke is the result either of a coagulation of the left ventricle or else of a disturbance of the innervation of the heart by an action of the heat upon the nerve-centres in the base of the brain; second, that these two forms of death correspond to sthenic and asthenic varieties of insolation—varieties which, I believe, have no proper existence.
9 Virchow's Archiv, t. lxii.
10 St. Bartholomew's Reports, vol. vii.
11 Archives générales de Médecine, Fèvrier, 1870.
The first experiments of Claude Bernard upon the action of external heat were given in a lecture upon muscular respiration on May 3, 1864, published in his Leçons sur les Propriétés des Tissus vivants (Paris, 1866). They were merely incidental to another research, and simply showed that when a warm-blooded animal was exposed to heat it died, the death being, according to the observations of Bernard, the result of cadaveric rigidity suddenly attacking the heart. The more elaborate researches of Claude Bernard upon the effect of exposure of animals to external heat, so far as I have knowledge, were not published in detail until after the nature of sunstroke was determined, although the lectures were delivered in the years 1871 and 1872; they may be found reported in full in his Leçons sur la Chaleur animale, sur les Effets de la Chaleur, et sur la Fièvre (Paris, 1876).
It is proper also to state here that some of the physicians of India had previous to this time more or less imperfectly recognized the relation of sunstroke to fever, but, I believe, none of them distinctly postulated the theory.
The above historical sketch shows that by many authors the relation of sunstroke to fever had been more or less dimly perceived, and that George B. Wood had very clearly stated the true nature of the affection, in that it was simply the result of the direct action of heat. Such statement, however, not resting upon proof, had not been accepted: it was also wanting in detail, and where such details were attempted the surmises were not always correct. Under these circumstances my researches, made in 1870 and 1871, and first published in 1872, led to the complete understanding of the affection.
The space allotted to me in the present volume will not allow of any detailed account of my experiments, but I shall quote from my summing up of the results obtained by them. It was shown that sunstroke may be produced in animals as readily as in man either by natural or artificial heat; that the symptoms are similar to those seen in man; that death takes place ordinarily by asphyxia; that after death the characteristic lesions are alteration of the blood and rigidity of the heart, with immediate or quickly-appearing post-mortem rigidity of the general muscular system; that this rigidity of the heart comes on in most cases after, not before, death, and is a result, not cause, of death; that post-mortem rigidity is dependent upon coagulation of myosin, and that the rigidity of the heart is of similar origin, coagulation of the muscle-plasma occurring almost instantaneously at 115° F., a degree almost attained in sunstroke; that when a muscle has been in great activity immediately before death, myosin coagulates at a much lower temperature, and that the cases of sudden cardiac death occurring in battle among the East Indian English troops were no doubt due to the coagulation of the heart's myosin; that heating the brain of a mammal produces sudden insensibility, with or without convulsions, at a temperature of 108° F., and death when a temperature of 113° is reached; that this effect of the local application of heat is not due to induced congestion, but is the result of the direct action of the heat upon the cerebrum, and that consequently the nerve-centres are as perniciously affected by high temperature as the muscles are; that the nerve-trunks bear a temperature of 125° F. without their conducting power being immediately affected; that whilst the general symptoms induced by heating the brain of a rabbit are very different from those of sunstroke, the nervous symptoms are exactly similar; that the life of the blood is not destroyed by any temperature reached in sunstroke, the amœboid movements of the white blood-cells and the absorption power of the red disks not being injured; that the amount of oxygen of the blood is greatly lessened, as the result of gradual asphyxia combined with abnormal consumption of oxygen; that there is no reason for believing that capillary thrombi are common in sunstroke; that there is no specific poison developed in the blood; that the deterioration of the vital fluid is due to the rapid tissue-changes induced by the fever and the more or less complete arrest of excretion; that such deterioration is secondary to the nervous symptoms, not primary; that if the heat be 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.
As a postulate from these facts and deductions, I think it follows that the nature of sunstroke is that of a fever; or, in other words, that coup de soleil is a fever, not dependent upon blood-poisoning, but upon heat.