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

by Southwood Smith

416. When the phenomena that take place in the opposite condition of the lungs were investigated, results were obtained which present a striking contrast to those which have been stated. On forcing into the lungs the largest quantity of air which they are capable of containing without the rupture of the air vesicles, and in this manner communicating to them the greatest degree of dilatation compatible with their integrity, it was found that in this state there passed through them only three drachms of blood.

417. But on fully distending the lungs with water instead of air, the pulmonary circulation was instantaneously and completely arrested; they were incapable of transmitting a single drop of blood. On cutting the aorta across, as in all the preceding experiments, not a particle of blood was obtained, excepting what issued at a single jet, and which consisted only of the blood contained in the vessel at the moment the respiration was stopped.

418. From these experiments it follows—

1. That the state of inspiration is favorable to the passage of the blood through the lungs. In the dilatation of inspiration they transmitted nearly double the quantity that passed in the collapse of expiration; or, as four ounces and five drachms are to two ounces and seven drachms (410 and 411).

2. That no degree of collapse to which the lungs can be reduced is capable of wholly stopping the flow of the blood through them. In the collapse of suspension and submersion they transmitted as much blood, with the exception of two drachms, as when death was produced by a blow on the head (412 and 409). In the greatest degree of collapse capable of being produced by an exhausting syringe, they transmitted half as much as in the collapse of suspension and submersion (414 and 412).

3. That it is only a moderate degree of dilatation that is favorable to the transmission of the blood through the lungs. When the lungs are over-distended with air, they are capable of transmitting only an exceedingly small quantity of blood ([416]); when they are fully distended with water, they are incapable of transmitting a single drop of blood ([417]). In fact they can contain only a certain quantity of air and blood; and when either of these fluids preponderates, it can only be by the proportionate exclusion of the other. It will appear hereafter that these results are capable of applications of the highest interest and importance in the explanation of numerous phenomena of health and of disease.

419. Physiologists have laboured with great diligence to determine the exact quantity of air and blood which enters and which flows from the lung at each of the actions of respiration, and they have succeeded in obtaining tolerably precise results.

420. The quantity of air capable of being received into the lungs of an adult man, in sound health, at an inspiration, is determined with correctness by an instrument constructed by Mr. Green, analagous to one suggested by Mr. Abernethy. It consists of a tin trough, about a foot square, and six inches deep, three parts of which are filled with water. Into this trough is placed a three-gallon glass jar, open at the bottom, and graduated at the side into pints, half-pints, &c. To the upper end of the jar a flexible tube is affixed, having at its connexion a stop-cock. The lungs being emptied, as in the ordinary action of expiration, and the mouth applied to the end of the flexible tube, the nostrils being closed by the pressure of the fingers, the air is drawn out of the jar into the lungs by the ordinary action of inspiration. When as much air is thus drawn into the lungs as the air vesicles will hold, the stop-cock is closed, and the quantity of air inspired is ascertained by the rise of the water, the level of the water corresponding with the indications marked on the side of the jar.

421. The quantity of air which a person by a voluntary effort can inspire at one time is found, as might have been anticipated, to be different in every different individual. These varieties depend, among other causes, on the greater or less development of the trunk, on the presence or absence of disease in the chest, on the degree in which the lung is emptied of air by expiration previously to inspiration, and on the energy of the inspiratory effort. The greatest volume of air hitherto found to have been received by the lung, on the most powerful inspiration, is nine pints and a quarter. The average quantity which the lungs are capable of receiving in persons in good health, and free from the accumulation of fat about the chest, appears to be from five to seven pints. The latter is about the average quantity capable of being inspired by public singers.

422. But these measurements relate to the greatest volume of air which the lungs are capable of receiving, on the most forcible inspiration which it is possible to make, after they have been emptied by forcible expiration, and consequently express the quantity received in extraordinary, not in ordinary inspiration. The quantity received at an inspiration easy, natural, and free from any great effort, may be two pints and a half, but the quantity received at an ordinary inspiration, made without any effort at all, is, according to former observations which referred to Winchester measure, about one pint.