The first column contains the heights be tween five and six feet, increasing arithmeti cally two inches at a time, as 1. 3. 5., &c. ; the next two columns are the result of ex periment ; the first upon 1012 cases at an earlier period of the investigation ; the next at a later period, when the whole cases con joined amounted to 1923 cases. We found that the men from 5 feet to 5 feet 2 in. gave a mean vital capacity of 176 cub. in.; the men two inches taller a mean of 191 cub. inches ; the next, 207 cub. in., and so on ; thus the volume increases as we descend the column. Finding the progression so regular, we arranged a fourth column, containing a series of numbers in perfect arithmetical progression, commencing with 174, and increasing sixteen at every subse quent step, corresponding to the two inches of height successively added. We found, upon comparing the two columns of observations with the column of calculation, that there was a close resemblance. The increase of sixteen for every two inches is of course the same as eight for every single inch ; hence the rule deduced upon nearly 2000 cases (and subsequently confirmed by double that number) viz. That for every inch of stature, from 5 feet to 6 feet, eight additional cubic inches of air, at 60°, are given out by a forced expiration.
This brings the detailed matter of a series of tables and calculations into a point, and easy of remembrance, the more so as extended ob servations upon nearly 5000 men have brought the column of observation so close to the column of regular progression, that it is only necessary now to take the column of regular progression as a standard for examining the condition of the lungs as to their perme ability for air, and the mobility of the tho racic boundaries.
If we recollect that at the height of 5 feet, 8 in. the vital capacity is 230, we can recollect the rest by adding or subtracting eight to or from this number, for every inch of stature above or below 5 feet 8 in., between 5 and 6 feet. These numbers may be taken as expressions of certain conditions of the thorax, an expression of mobility relative to breathing, and conse quently an expression of the permeability of the lung. It therefore follows that whatever affects the mobility of the thoracic bound aries, or the permeability of the lungs, the amount of that cause is expressed by the volume of the vital capacity. Incipient disease is quick in affecting the vital capacity ; the amount of the injury therefore is readily measured. We are at a loss to assign any just reason why the vital capacity is rela tive to the height, which is regulated by the length of the limbs, and not by the length of the trunk of the body. We have found by experiment, that whatever be the standing height, the sitting height is nearly the same in all persons of between Sft. and 6ft., and if not actually the same, yet it is not a rule that the tallest men sit the highest ; for in stance, one man standing 6ft. Olin. measured from his seat 2ft. 11-gin., whlie another who
stood 5ft. 6in., sat Mt. high ; therefore the length of the trunk bears no constant propor tion to the length of the legs. And we found that men who stood low, breathed less than men who stood higher, but who sat the same height. Thus fig. 706. represents two men ; A. stood 4ft. 4-tin., B. 5ft. 9k-in.; they were of the same age and circumference of the chest. The weight of the short man was 7st. 211b., that of the taller man 10st. 31b. Yet their sitting height was precisely the same, as is shown in fig. 707. Nevertheless, the vital capacity volume of the shorter man was 152, and that of the taller man 236 cubic inches; so that the man who stood the shorter, but who sat as tall, if not taller, breathed eighty four cubic inches less than the man who stood seventeen inches higher. The mobility of the chest of the taller man was ',early four inches, that of the shorter man three inches. We ex amined several such cases with similar results. The average vital capacity volume at all heights, is about 230 cubic inches. The greatest we have examined was Randall's ; height 7 ft. weight 22st. ; vital capacity 464 cubic inches. The smallest was Don Francisco; height 29 in., weight about 401bs. ; vital capacity 46 cubic inches. The highest vital capacity at the height of 5ft. Bin. was 330 cubic inches.
A question arises, are the lungs and tho racic parietes at their maximum stretch when they contain the appropriate vital capacity volume ? We believe not. The vital capa city of the person from whom the preparations figured above (figs. 680. et seq.) were taken, whose height was 5ift. 4 in., weight 107 lb., was 198 cubic inches ; yet, after death, we forced 300 cubic inches of air into his lungs without rupturing them, being 102 cubic inches more than he could expire during life. There fore there is still a spare mobility of parts, probably in reserve, to be exercised when dis ease attacks the lungs.
2nd. Vital capacity affected by the posi tion of the body. — We have said a man must hold himself erect to breathe out a good vo lume of air ; because the mobility of the ribs is affected by the uprightness of the spine ; and, more than this, whatever touches the ribs affects their mobility, and consequently the vital capacity. Thus, standing, we have produced a vital capacity of 260 cubic inches ; sitting erect 255 cubic inches; recumbent supine 230, prone 220 cubic inches ; position making a difference of 40 cubic inches. This may explain why patients with emphysematous lungs sit up in bed, and why for them to lie recumbent, is " suffocating ;" because they thereby diminish the thoracic mobility. It may be well to recollect this effect upon respi - ration, in treatment of diseases of the spine, particularly at the present time, when they are treated by laying the patient on the anterior part of the chest for weeks and months gether, which position reduced our vital ca pacity from 260 to 220 cubic inches.