OF THE ELASTICITY OF THE RIBS. - Elasticity depends upon reaction, and restores in a contrary direction the force which have been impressed ; the effect produced is com mensurate with the amount of the cause, and the reaction can never take place so long as the cause continues to be applied ; but immedi ately that cause ceases, the elasticity comes into action.
Inspiration is performed by the true inspi ratory muscles, and expiration, by the expira tory muscles, and the elasticity of the ribs and their cartilages, together with the elasticity of the lungs. We find a broad difference manifested between the inspiratory and ex piratory power (TABLE R.), the latter exceed ing former by about one third. This differ ence is due to the elasticity of the ribs and lungs associating their power with the ex piratory muscles. The combined elastic power is very great ; we have examined it in two fa vourable cases, an hour after death, when the bodies bad not fallen one degree in temperature.
X. H., a young man, slightly built, erect and well formed, mt. 22, weight 91st., height 5ft. 10in., vital capacity 235 cubic inches. The absolute capacity of his chest was 248 cubic inches ; internal area 256in.; circumfe rence of the chest, over the nipples, in the or dinary state, alive 33 inches, dead 301 inches. After death we forced air into his lungs, whilst the temperature of the body was still at 97°. The force resisting the introduction of this air must havebeen due to the elasticity of the ribs and their cartilages, together with that of the lungs. By an arrangement, we could force in different quantities of air, and measure the collapsing power of the elastic parts, through the medium of the confined air pressing upon a column of mercury : the following was the result :— We could not force in more air, for with this pressure it was impossible to prevent the air escaping with great rapidity through the ne cessary wounds. This experiment was re peated three times with the same result. It will be remembered that X. H. had drawn into his lungs, when alive, 75 cubic inches of air more than we could force in, after death. If, therefore, 160 cubic inches pro duced a collapsing elastic force equal to 2.5 we may suppose that 235- cubic inches would produce an elastic force equal to not less than 3.9 in. of mercury. This chest, mea suring 256 superficial square inches, it fol lows that X. H., in breathing out 235 cubic inches of air, with no more sensible effort than that of a mere sigh, had to overcome with his inspiratory muscles a gross elas tic resistance of about 4991bs., and with a
force equal to this weight would the thoracic walls recoil for expiration upon the air in his lungs.
N. C., height 5ft. 8in., weight 10st. 101b., mt. 21: vital capacity, 200 cubic inches; ab solute capacity, 245 cubic inches; superficial measurement of the entire thoracic cavity, 256 square inches ; circumference of the chest, alive, 33 inches, dead, 344. Temperature of the body, when examined, 97° F. Tempera ture of the air forced into the lungs, 63° F. This man was what is termed " thick set," firm, erect, and well built, a porter by trade, a very different case from the former. The fol lowing was the elastic power of his ribs : — The first ninety inches of air introduced ruptured the lungs ; therefore the elasticity of the lungs did not interfere with our experi ments. In both cases this resistance must be referred only to the ribs, their cartilages and ligamentous attachments ; also, in both cases, the bodies were kept erect, or in the sitting posture ; this should be attended to, for the mere weight of the body upon the ribs when recumbent would increase their collapsing power.
These tables express a dead power al ways in reserve, equally powerful whether we are in robust health, or emaciated by age or disease. Dead or alive, this is ready to be put into force ; and, in fact, it is never at rest, never at zero, until death ; we may even go farther, and say, not until de composition has weakened the collapsing ten sion of these parts. Cut through a costal cartilage, or take out a small portion of the sternum, say corresponding to the 3rd, 4th, and 5th intercostal spaces, and the opening by the elasticity of parts will retract, and we never can restore them again to their original fit, because the thoracic parietes are still not at rest. The bony cage-work of the chest is so tightly knitted together, that at its mini mum contraction there still remains an elastic force in operation. In fact we might expect this, because the respiratory movements are so small that it is necessary that an extensive elastic power should be ready at all the re spiratory stages ; and therefore the parts are upon the stretch before we begin to inspire in order to increase to the geometrical degree re quired, of two, three, or four pounds to the inch, by a very limited movement, which would not be the case did we begin to in spire when the thoracic boundaries were at zero, at least, if it did, the walls, &c., would have to be much stronger.