It is of course possible that the external heat causes the fever, simply by preventing the body from throwing off the caloric which it is constantly forming. The extreme suddenness of the onset, however, indicates that in at least many cases there is a sudden outburst, as it were, in the production of heat in the body. This indication becomes more important when it is remembered that in cerebral rheumatism, so called, there is often an equally sudden attack of symptoms plainly the result of a sudden production of animal heat.
In an elaborate research12 I showed the truth of Setschenow's theory, that there is in the pons a centre whose function it is to inhibit the production of animal heat, and that in the medulla a centre (probably the vaso-motor centre) which regulates the dissipation of the bodily heat; and that fever is due to disturbance of these centres, so that more heat is produced than normal, and proportionately less heat thrown off. Let it be supposed that a man is placed in such an atmosphere that he is unable to get rid of the heat which his body is forming. The temperature of his body will slowly rise, and he may suffer from a gradual thermic fever. If early or late in this condition the inhibitory heat-centre becomes exhausted by the effort which it has been making to control the formation of heat, or becomes paralyzed by the direct action of the excessive temperature already reached, then suddenly all tissues will begin to form heat with the utmost rapidity, the bodily temperature will rise with a bound, and the man drop over with some one of the forms of coup de soleil.
12 Fever, Smithsonian Institute, 188-.
Under this view of the case the widespread popular belief, that protecting the back of the head and upper neck from the direct rays of the sun is useful against sunstroke, gains in significance, because it is possible that local heating of the parts spoken of may occur and aid in the production of inhibitory paralysis.
If this theory of thermic fever be correct, heat-exhaustion with lowered temperature probably represents a sudden vaso-motor palsy—i.e. a condition in which the exhausting effects of the heat paralyzes not the inhibitory heat-centre, but the vaso-motor centres in the medulla, since my experiments have shown that vaso-motor palsy increases enormously the loss of animal heat and diminishes its production.
In most cases of sunstroke death comes on gradually by arrest of respiration, such arrest being without doubt due to direct paralysis of the respiratory centres by the excess of heat. Allusion has already been made to the cases of sudden death by cardiac arrest, which have especially been seen in India, almost always during a march or during a battle. “As an example of it may be cited the account given by a witness to Parkes, and incorporated in his work on hygiene,13 of an occurrence during the first Chinese war. The Ninety-eighth regiment was marching on a very hot day, and the surgeon who was with the rear-guard stated to Parkes that the men fell suddenly on their faces as though struck with lightning, and on his running up and turning them over many of them were already dead. Maclean, who was present at this occurrence, confirms the account given by Parkes, but states that it was at the attack on Chiang-Kiang-Foo. The men were thickly clothed, with tight accoutrements and tight, rigid stocks, and were charging up a very steep hill. A great number of them were stricken down, and fifteen died instantly, falling on their faces and giving merely a few convulsive gasps.”
13 Pract. Hygiene, 2d ed., p. 360.
It has been shown that excessive exercise so alters the condition of the myosin of muscle as to cause it to coagulate much more readily than normal. During battle the amount of muscular effort that is made is enormous, and hence it is that men are so often found stiffened in the attitude in which they were struck by the bullet, instantaneous death being followed by equally instantaneous post-mortem rigidity. The description that has been given by Parkes and Maclean of the circumstances in which the sudden deaths just described occurred shows that the heart-muscles must have been strained to their utmost limit. The men were making violent exercise going up hill, so that the heart must have been in exceedingly active exertion, increased by the impediment to the circulation afforded by the tight accoutrements, and under these circumstances the victims probably died instantly because the heart-muscle suddenly set itself from life into the stiffness of death.
The DIAGNOSIS of thermic fever is usually made with great readiness. In distinguishing between it and heat-exhaustion the temperature of the body is the guide. In apoplexy with high temperature it is possible that a little embarrassment might be experienced, but in apoplexy the high temperature follows the nervous symptoms after a distinct interval, but in thermic fever it precedes the unconsciousness. An apoplexy may develop during a sunstroke, but such occurrence is rare. T. S——, now under my care, has had frequently repeated attacks of local convulsions affecting two fingers of the right hand, and one general epileptic attack whilst under observation. He dates his illness to a sunstroke on July 7, 1885, and O. D. Robinson of Georgetown, Delaware, writes me that the attack was undoubtedly true thermic fever, and that the movements of the fingers came on whilst the patient was recovering consciousness. It is probable, therefore, that there was a rupture of a small vessel in the brain-cortex during the sunstroke. The appearance of local convulsions or of localized paralysis during a sunstroke would be good ground for believing that either a clot or a thrombus had formed.