A little more attention to the subject, it appears to me, could have spared the authors quoted above a great deal of perplexity in explaining, or rather in attempting to explain the phenomenon so often mentioned, regarding the rise of the body temperature before and soon after death. They have, it appears to me, entirely left out of consideration the fact, that there must be stored up in the living tissues of an animal a considerable amount of potential energy in the shape of irritability. Let us study for a moment the life and death of a muscle. When a living muscle is made to contract, oxygen is absorbed and carbonic acid and water is set free; muscular contraction, as a consequence is invariably accompanied by heat production; and there can hardly be any doubt that the heat thus set free is the product of chemical changes within the muscle. In fact a muscle may be likened to a steam-engine in which combustion of a certain amount of material gives rise to the development of energy in two forms: in the form of heat and in the form of motion. A similar process of combustion is, however, slowly and continuously carried on in every living muscle, even when at rest. For even when the muscles are at rest the blood which leaves them by the veins contains more carbonic acid than the blood even of the right ventricle so that a living muscle may be looked upon, as a constant heat- producer, the heat-production being only less in degree when at rest, than when at work. This silent activity of a living muscle is known by the name of tonicity, a condition met with in every healthy muscular tissue, and what becomes of a muscle in the case its supply of oxygen be withdrawn, the blood circulating within its tissue being rendered venous? In that case, experience teaches, that the venous blood acts in a measure as a foreign body, stimulating, for a time, the muscle to contraction; and when that contraction has ceased, then the irritability of the muscles is lost; it ceases to respond to stimulation of any kind. Irritability and tonicity are then two essential qualities of living muscular tissue; both of them may be considered as the expression of a certain molecular work going on within the tissue. In the same way are we entitled to look upon two other known qualities of living muscular tissue-elasticity and extensibility. The maintenance of all these vital properties depends no doubt upon the continuance of that mode of molecular work peculiar to life.
For all these properties gradually cease with the approach of, and shortly after, death. Muscular irritability diminishes with the setting in of rigor mortis, and when the same is complete, irritability has ceased to exist. Something similar occurs with regard to tonicity, elasticity and extensibility. The dead muscle, for instance, when extended does not return to its previous length. There is then a certain amount of energy latent during life, in the shape of molecular work, which is gradually set free by death, and, in obedience to the law of Conservation of Energy makes its appearance in another form of energy-in the form of heat.
What has been said with regard to muscles, might, by a somewhat analogous reasoning, by applied to all the other tissues and organs of the body; for irritability is common to all living matter although the mode of its manifestation differs with every organ. Then there are the centres of automatic activity seated within the spinal column; there is further a constant activity of unconscious cerebration going on during life; all this represents a certain amount of potential energy, which is liberated in consequence of death in the form of heat. The post-mortem rise of temperature is as little perplexing a phenomenon to me, as the phenomenon of a liquid body giving out heat during the process of solidification would be to any one acquainted with the laws of physics.
Of course, what I have said in explanation of the post- mortem rise in temperature, refers to the period preceding the setting in of rigor mortis; for with the same, there is ample ground for increase of heat, as the muscular contraction, or as Carpenter correctly states it, the passage of a muscle into the state of contraction, is under all circumstances connected with heat-production.
All this way yet be far from explaining the extra-ordinary post-mortem rise of temperature in victims of cholera, yellow fever and tetanus. But unless we learn first to understand the nature of the ordinary phenomenon, it would be a hopeless task to speculate upon some of its exceptional phases.
As to the extraordinary amount of heat evolved in the case of cholera victims, I must say, the difficulty with me is not so much to understand, why there is a post-mortem rise in temperature, but why there should be a considerable fall of temperature during the whole course of the disease, seeing that the same is generally accompanied by spasmodic muscular contraction, and knowing as we do that such contractions are always attended by evolution of heat, in fact are looked upon as the chief caloric source of the living body.
Tetanus is associated with a temperature as high as 3 degree to 4 degree above the normal standard, owing to this very state of muscular contraction; why should then cholera be characterised by a temperature below the normal standard? The only explanation I am able to suggest consists in the following considerations.
True as it is that a muscle may be likened to a steam engine, in which the combustion of a certain amount of material give rise to the development of energy in two forms: heat and motion; the relation between the amount of energy set free as heat and that set free as mechanical work is, in the case of a muscle, not under all circumstances the same. The proportion between heat and work varies moreover to such an extent that the work amounts in some cases to one fourth and in other cases to one twenty-fourth of the total energy set free by the chemical process of oxidation within the muscle.(*See M.Foster’s Text Book of Physiology, London, Macmillan & Co. 1883. P.67.*) Muscular contraction can then under certain circumstances be carried on more or less economically, that is to say, a comparatively small quantity of liberated energy, may be made to effect a considerable amount of muscular contraction, provided the energy liberated be mostly utilised in the form of motion (contraction), and that as little as possible be allowed to run waste in the form of heat.
Now it appears to me that in this fact lies an un-thought of explanation, of the phenomenon known as the maintenance of the mean temperature in worm-blooded animals. As you are aware, gentlemen, warm-blooded animals maintain, under all varieties of atmospheric temperature, the same degree of body heat; and there are various contrivances within the organism which contribute to the keeping up of an equable temperature within certain limits.
Foremost of them are such arrangements as regulate the elimination of heat. Increased temperature causes dilatation of the small arteries of the skin, whereby more blood is made to circulate at the surface of the body, which leads to an increased loss of heat by conduction and radiation. The secretion of sweat is, moreover, either occasioned or increased in quantity by an increased fulness of the vessels of the skin and the rapidly evaporated sweat consumes an extraordinary amount of heat. Then there are such arrangements as exert their action in regulating the production of heat. Living in a cold atmosphere increases the feeling of hunger and increased consumption of food augments the production of heat. Then again when the body is exposed to cold the need for muscular exertion is felt, and this raises the temperature.
Now the very fact that increased muscular action-voluntary or involuntary-augments the body temperature, necessarily implies that during the act of muscular contraction more heat is produced than is consumed by its being converted into mechanical work. The proportion between the two, between the energy liberated as heat and the energy liberated as work, depends as we have seen before, on various circumstances. Is it then not natural to expect that the maintenance of the mean temperature in warm-blooded animals should, at least partly, be owing to a certain adjustment of the before mentioned proportions? There evidently exists some regulating agency within the living body of warm-blooded animals, by which production and elimination of heat is constantly balanced; and although the exact seat of that agency may not have been as yet clearly pointed out, there is perfect unanimity between physiologists that such a regulating centre does exist. Such being the case, it would be strange, should the proportions between muscular energy liberated in form of heat, and muscular energy liberated in form of work, not fall under the regulating administration of the caloric centre.
We may then fairly assume that one of the contrivances of the organism for maintaining its temperature within certain limits under considerable variations of temperature of the surrounding atmosphere, consists in this, that in a hot atmosphere muscular work both mechanical and molecular is carried on in a proportionately economic way; that is to say, there is comparatively much work done with comparatively little waste of energy in the form of heat; while the reverse is the case in a cold atmosphere. And it is the function of the caloric centre to regulate the respective portions of work (mechanical or molecular) and heat originated within the muscular tissue.
