3rd. Vital capacity affected by weight. The weight affects the vital capacity ; but as yet the relation does not appear so regular as that of the height. We are scarcely in a position, at present, safely to say much upon this point. As a general rule we find the weight increases with the height ; so that it is not easy to separate the effect of one from that of the other. Suppose we take two men of the same stature, say 5 feet 8 inches, the one 10 stone, the other 14 stone in weight ; one of them above par, the other may be either at, or below par. If 10 stone be considered par, the 14 stone man is 4 stone in excess, or corpulent to 40 per cent. This excess weight blocks up the range of mobility, and thus, mechanically, diminishes the vital capacity volume. But let us suppose men of dissimilar heigths, one 5 feet 8 inches and the other 6 feet ; the 6 foot man should be heavier than the shorter man ; — say 3 stone heavier. This is not excess weight with him, and does not interfere with his thoracic mobility ; therefore there is an inseparable relation between the height and weight. If, in a series of experiments, we sink the height entirely, and keep the mere weight in view, we shall find that the result as to the vital capacity volume is without order.
next from 5 feet 1 inch to 5 feet 3 inches, taking their mean as 126.1 lbs., and so on. • It thence follows, the range of stature from 5 feet 1 inch to 5 feet 11 inches is 10 inches ; and the weight rises from 119-9 lbs. to From this there is seen to be a rude increase of the vital capacity with the increase of the weight, but it is quite irregular, as 21., 12., 23., &c. We have also found the mean vital capa city of 147 men of 11 stone as 225 cubic inches, and that of 32 men of 14 stone, only 233 cubic inches, an .increase of 8 cubic inches for an increase of 42 lbs., or 3 stone. The over whelming effect of height disturbs the above observation ; therefore the height must be kept in view. We have calculated the weights in relation to height, with reference to the res piratory function, upon a number of men at the middle period of life. Besides the three classes mentioned above, we have included 1554 cases of healthy men in the prime of life, oblig ingly furnished by Mr. Brent, viz. the Oxford and Cambridge rowers, London watermen, cricketers, pedestrians, and gentlemen (TABLE X). The weight now appears more regular, increasing with the height, as from 92 lbs. to 218 lbs. We may make this progression ap pear more regular, as in TABLE Y, which is calculated by adding the mean weight, from the last table, of the men from 5 feet to 5 feet 2 inches (the mean of which is of course 5 ft. 1 in.), together, and taking the mean of that, which will be found 119.9 lbs. ; and the 174.2 lbs., or 54'3 lbs. ; or 5'43 lbs. with every inch of stature. To subdivide the range of height it may be said :— There is an inequality from 5 feet 4 inches to 5 feet 7 inches in the weight ; but this would in all probability disappear if the ob servations were more extended ; at present it may be stated generally that the weight in creases 6.5 lbs. (or 62 lbs.) for every inch of stature from 5 feet 7 inches to 6 feet, and 6.2 lbs. for every inch of stature from 5 feet 1 inch to 5 feet 4 inches, and 3.3 lbs. for every inch from 5 feet 4 inches to 5 feet 7 inches. • At 5 feet 8 inches, or 68 inches of stature, the weight is 155'2 lbs., or nearly 11 stone;
from this as a starting point the weight at any height may (so far as our limited ob servations warrant) be readily calculated. For instance, the weight is, at the height of 5 feet 8 inches, .282 lbs. for every inch stature, or 27'38 lbs. for every foot of stature. The bulk or weight of bodies having the same relative proportions, is as the third power (cubes) of either of their diameters : thus, if a person 67 inches high weighs 148.44 lbs., a person 69 inches high should weigh (69-) 3 X X 69 X 69 67 67 x 67 x 67 X 118.44=303285090763 x 148.44=162.14 lbs. The weight at that height, from observation, was 162.08 lbs., a similarity too close to be acci dental.
The weights vary as the 2.75th power of the height, and not as the 3rd power. The rela tion between the two is quite close enough to show, that there is a very intimate connec tion between the height and the weight. The observation is made upon 1276 men at the middle period of life.
We have found that the vital capacity in creases 42 cubic inches with the weight from 100 lbs. to 1551bs., and from 155 lbs. to 200 lbs. the effect is balanced by minus 5 and plus 5 cubic inches. In the first division there is an increase of 42 cubic inches ; the weight then comes into power, and disturbs the regular progression for the next division ; therefore we may say there is in the second division a de crease of 42 cubic inches in the vital capacity volume from the effect of weight. We repre sent this by a curve,fig. 708. The continuous curve is the line of vital capacity crossing the perpendicular lines of progressive weights. The curve of volume ascends, and attains its highest at 160 lbs., and from thence it is nearly horizontal to 200 lbs. According to this, the vital capacity increases nearly in the ratio of 1 cubic inch per lb. from 105 to 155 lbs., and from 155 to 200 lbs. there is no increase. This illustration of the effect of weight is cal culated at one height, viz. 5 feet 6 inches ; therefore to this height only thesepoints of weight (from 11+ to 14 stone) refer. We have noticed that the weight increases in a certain ratio with the height, and that the weight at 5 feet 6 inches affects the vital capacity in the relation just mentioned, com mencing when the weight exceeds 7 per cent upon the average weight. We may, perhaps, connect this same relation with the other heights through the arithmetical progression of inch by inch. For example :— the weight of men of 5 feet 1 inch is 199.9 lbs. ; to this add 7 per cent (8'395 lbs.), making 128.2 lbs. ; again, the tallest men, 5 feet 11 inches, weigh 174-2 lbs. ; to this add 7 per cent (12.2 lbs.), making 186.4 lbs.: therefore, at the height of 5 feet 1 inch a man must exceed 128 lbs., or 9 stone 2 lbs., and the 5 feet 11 inches' man 186 lbs., or 13 stone 4 lbs., before weight may be expected to diminish the vital capa city volume in the relation of 1 cubic inch per lb. for the next 25 lbs., 2+ stone being the limit of our calculation. When the man exceeds the mean weight (at each height) by 7 per cent, the vital capacity decreases 1 cubic inch per lb. for the next 35 lbs. above this weight. Beyond this it is not improbable but that the decrease of the vital capacity is in some geometrical progression. Below the mean weight we have never found by experiment, that the vital capacity is affected by weight.