. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. THORAX. 10G3 cury is sustained, the force exerted by the diaphragm alone is equal to the weight of as much mercury as it would take to cover a space of the same area as the diaphragm, three inches deep. The column of mercury raised, therefore, will not safely serve to compare the respiratory power of men of different dimensions, for the area of the thorax must also be considered. For instance, we examined a man, 4 feet 74inches high (circum- ference of the chest 29 inches), who raised 3'15 inches; and another man, 7 feet
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. THORAX. 10G3 cury is sustained, the force exerted by the diaphragm alone is equal to the weight of as much mercury as it would take to cover a space of the same area as the diaphragm, three inches deep. The column of mercury raised, therefore, will not safely serve to compare the respiratory power of men of different dimensions, for the area of the thorax must also be considered. For instance, we examined a man, 4 feet 74inches high (circum- ference of the chest 29 inches), who raised 3'15 inches; and another man, 7 feet high (chest 50 inches in circumference), who could only elevate 3 inches of mercury: but the dissimilarity between the area of the dia- phragm in the dwarf and giant was such, that the latter in reality lifted about 500 Ibs., and the former only about 39 Ibs. Suppose the base of his chest to be 57 superficial square inches ; had this man raised 3 inches of mercury by his inspiratory muscles, his diaphragm alone must have opposed a resist- ance equal to more than 23 oz. on every inch of that muscle, and a total weight of more than 83 Ibs. Moreover, the sides of the chest, by attenuating the air within, resist an atmospheric pressure equal to the weight of a covering of mercury 3 inches in thick- ness, or more than 23 oz. upon every inch surface, which, if we take at 318 square inches, the chest would be found to resist a pressure of 713 Ibs. ; and, allowing the elastic resistance of the ribs as inch of mercury, this will bring the weight resisted by the inspiratory muscles of the thorax as follows: — Diaphragm - Walls of the chest Costal resistance (elastic) Lung - 1146 Or, in round numbers, we may say, that the inspiratory muscles of such a man of ordinary dimensions resisted 1000 Ibs. This is a re- sistance not counterbalanced; for were it counterbalanced, it would only be mere dis- placement. We have made a safe addition for the elasticity of the lungs. We think
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