The Philosophy of Health; Volume 2 (of 2) / or, an exposition of the physical and mental constitution of man

by Southwood Smith

521. Inspiration favours the flow of blood to the lungs; expiration retards it: consequently, if from any causes the inspirations preponderate in number and proportion over the expirations, a greater quantity of blood than usual will be accumulated in the lungs. There are conditions of the system in which this preponderance of the inspirations actually takes place; when the mind is under the influence of certain emotions, for example, as when it is depressed by anxiety and fear. In this state the inspirations are more frequent

and more complete than the expirations; it is a state of continual sighing. In like manner, in certain diseases, such as asthma, the inspirations greatly preponderate both in frequency and energy over the expirations. In such conditions of the system the blood accumulates in preternatural quantity in all the internal organs; but more especially in the lungs; and two consequences follow: first, there is a remarkable diminution in the energy of all the vital actions; and secondly there is a proportionate diminution in the production of animal heat.

522. On the contrary, as it is the effect of inspiration to facilitate the motion of the blood through the lungs, so it is the effect of expiration to retard it; hence, when the expirations preponderate the opposite state of the system is induced; all the vital actions are performed with increased energy; the heart beats with unusual vigor; the pulse becomes quick and strong; a larger quantity of blood is determined to the surface of the body, and this excited state of the system is always attended with an augmentation of the temperature.

523. As in the first state there is a greater and in the second a smaller quantity of blood than natural contained in the lungs, the inference deduced by Dr. Holland is, that the production of animal heat is in the inverse ratio of the quantity of blood exposed to oxygen. But this inference is neither logical nor sound.

524. If, as a comparison of all the phenomena of respiration exhibited throughout the entire range of the animal kingdom, shows the production of animal heat to be in the direct ratio of the quantities of air and blood which are brought into contact, and which re-act on each other, every phenomenon of respiration must be in harmony with this law, and, accordingly, when really understood, it is found to be so.

525. Inspiration, by the dilatation of the thorax, and consequently of the lungs incident to that action, is favorable to the flow of blood to the lungs. But it is only a certain degree of dilatation of the lungs that is favorable to the flow of blood through them (407 et seq.). If the dilatation be carried beyond a certain point, the quantity of blood transmitted through the pulmonary tissue is diminished ([406]); if the dilatation be carried farther, the transmission of the blood may be wholly stopped ([417]). The quantity of the blood which flows to the lungs, and the quantity which circulates through them, are not then identical. So large a quantity may flow to them as to impede or retard or wholly stop the pulmonary circulation. In proportion to the accumulation of blood in the lung must necessarily be the distension of the pulmonary tissue; in that proportion the lung must be approximated to its condition in the experiment in which it was distended with water ([417]), when it did not transmit a single particle of blood. Further, in proportion to the preternatural distension of the pulmonary tissue with blood must be the exclusion of air from the air vesicles for the lungs can contain only a certain quantity of blood and air (418.3), so that the blood can preponderate only by the exclusion of the air.

526. In those states of the system, then, in which the preponderance of the inspirations induces a preternatural accumulation of blood in the lungs, the production of animal heat is diminished for a two-fold reason; first, because the distension of the pulmonary tissue with blood retards the pulmonary circulation, and proportionally lessens the quantity of blood which is brought into contact with the air; and, secondly, because the distended blood-vessels compress the air vesicles, and so diminish the quantity of air which is brought into contact with the blood.

527. It follows that the diminution of temperature which takes place in this condition of the system is not because the production of animal heat is in the inverse ratio of the quantity of blood which is exposed to oxygen; but because from a two-fold operation there is a diminution of the quantity of blood and of oxygen which are brought into contact.

528. The reason is equally obvious why there is an increase of the temperature in those conditions of the system in which the expirations preponderate over the inspirations. Expiration, it is true, somewhat retards the circulation of the blood through the lungs, but the preponderance of this respiratory action does not raise the temperature by the retardation of the flow of blood through the lungs, and the consequent diminution of the quantity transmitted in a given time; for though expiration somewhat retards the circulation of the blood through the branches of the pulmonary artery, it promotes its circulation through the branches of the pulmonary veins (fig. [CXL]. 10). It is indeed by the action of expiration that the aërated blood is transmitted from the lungs to the left heart to be sent out renovated to the system. Expiration has no influence whatever over the aëration of the blood. Before the action of expiration takes place, the blood is already aërated. The office of expiration is to remove from the system the air which has served for respiration, and to transmit to the system the blood which has been subjected to respiration. Consequently, in those states of the system in which the expirations preponderate, the temperature is increased, not because the expiratory actions, by lessening the quantity of blood in the lungs, diminish the quantity exposed to oxygen, but because they transmit to the system oxygenated blood as rapidly as it is formed, that is, blood which either produces animal heat in the act of its formation, or which generates it as it flows through the system.

529. These conditions establish the conclusion deduced, as has been stated, from the comparison of the phenomena of respiration exhibited throughout the entire range of the animal kingdom. But if the production of animal heat be really the result of combustion, if that combustion take place in the lung, and if the lung be thus the focus whence the heat radiates to every other part of the body, why is not the heat of this organ and of the parts in its immediate neighbourhood higher than the temperature of the rest of the body? Some of the internal organs are indeed a degree or two hotter than the general mass of the circulating blood ([469]), and among these the lung is admitted to rank perhaps the very highest. But how can a quantity of caloric sufficient to maintain the heat of the body in a temperature of forty degrees below zero radiate from an organ the temperature of which is only two or three degrees above that of the body itself? It is estimated that, in every minute, during the calm respiration of a healthy man of ordinary stature, 26·6 cubic inches of carbonic acid, at the temperature of 50° Fahr. are emitted, and that an equal volume of oxygen is withdrawn from the atmosphere. From these data it is calculated that, in an interval of twenty-four hours, not less than eleven ounces of carbon are consumed. Why is the lung, the seat of this combustion, not only not greatly warmer than any other organ; but why is it not even consumed by the fire which is thus incessantly burning within it?