OF RESPIRATORY MUSCULAR POWER. Young falls into an error in supposing " that in muscles of the same kind the strength must be as the number of fibres, or as the extent of the surface which would he formed by cutting the muscle across ; and it is not improbable that the contractile force of the muscles of a healthy man is equivalent to about 500 lbs. for every square inch of the section."* When we examine men we find no such calculations are to be relied upon. It is very common to find two men of cor responding dimensions produce very different effects upon any dynamic instrument.
The respiratory power may or may not cor respond with the general development of mus cular force.
We have submitted 1500 men of various classes to an experiment upon the inspiratory and expiratory power. The resistance to this power was a column of mercury,—the heemady namonzeter, or bent tube, first used by Dr. Hales. He observes, "A man, by a peculiar action of his mouth and tongue, may suck mercury 22 inches, and some men 27 or 28 inches, high ; yet I have found by experience that, by the bare inspiring action of the dia phragm and dilating thorax, I could scarcely raise the mercury 2 inches." t Hales appa rently never tested the expiratory power.
We connected the column of mercury with the index on a dial plate, which represented the inches and tenths of inches of mercury lifted. A tube was adapted to fit the nostrils through which the inspiratory or expiratory effort was made. By the former the index was moved in one direction, and by the latter in the con trary direction; each half of the dial plate representing, respectively, inspiratory and ex piratory power, with expressive words at tached, as follow : — (See top of next page.) It will be observed that the figures on each side of the same word differ in their value, those of the expiratory side ranging about one third higher than those on the inspiratory side.
Indeed when these powers are the same, it indicates disease. We subjoin the following table of the result of these cases. (Table S.) To illustrate one of the points so striking in these experiments (viz., the difference be tween the inspiratory and expiratory power), we refer to diagram 701., which represents by curves their relative position. The upper line is the expiratory power, and the double line below, the inspiratory power. The per pendicular lines are the different heights of the cases examined. The position of these
curved lines indicates the power they re present, — the higher the curve the greater the power. The two rows of figures at the bottom are the inches and tenths of inches of mercury elevated. (I. for inspiration, and E. for expiration.) According to this, at the height of 5 feet 7 inches, and 5 feet 8 inches, the inspiratory power is greatest, and thence the inspiratory power gradually decreases as the stature increases. The men of 5 feet 7 inches and 8 inches elevate a column of 3 inches of mercury : this may be considered a healthy power ; and the men of 6 feet high elevate about 2/ inches of mercury as their healthy power.
It may be asked, why connect this with the height ? Because it was found in six collateral observations that this was the only physical condition which presented a relation so as to throw the experiments into an or derly position.* By TABLE S we see that the respiratory power varies in different classes. The "gentlemen," for instance, are below most of the other classes : at the height of 5 feet 8 inches, they elevate by inspiration 2.35 inches of mercury. This may account for the fact why Dr. Hales could only raise 2 inches of mercury by this effort.
The expiratory power is normally more irregular—more apt to vary—than the inspi ratory power. The expiratory muscles par ticipate in other duties besides that of mere expiration ; the vocation of the glass-blower, the trumpeter, the wrestler, the jeweller (blow-pipe), and the sailor, especially call these muscles into use, increasing their na tural power. They thus oftentimes become excessively strong. The inspiratory muscles are exclusively for supplying us with air, in which act they have only to oppose the uniform resistance of elasticity. The inspira tory rower is therefore the best indication of the "health"— the "vis vitw." As an instance of the effect of vocation chang ing one of the respiratory powers and not the other, we may notice the Metropolitan po lice and the Thames police. The inspiratory power of these two classes is nearly equal, whilst the expiratory power of the Thames police exceeds that of the Metropolitan police,—the former using their upper extre mities, whilst the latter use their lower ex tremities most : — the former chase the thief by the use of the oar ; the latter by the swiftness of their legs.