(b) Reserve volume. Goodwyn omits this volume altogether ; and this omission was pointed out forty years ago by a phy siologist who himself omitted any notice of the complemental air. Kite estimates this at 87 cubic inches; Davy, by an experiment upon" himself, at 77 cubic inches I ; Dr. Ros tock, from trials upon himself, at 160 or 170 §; Mechel at 110 cubic inches.I1 It averages about 100 cubic inches ; our obser vations range from 70 to 110 cubic inches. It is"regulated by the point at which the or dinary breathing movement commences.
(c) Breathing volume. This has attracted most attention ; but the discrepancies of opinion are nearly commensurate with the number of observations. It would require of labour determine this volume by direct experiment, in a manner to be avail able to the physician ; and it would re quire a long time to perfect the observation of it upon a single patient, because these movements are so delicately affected by the mind, so perfectly uncontrollable, and the volume is so small, that a little error would seriously damage the value of the observation. The volume assigned by observers, varying from 3 to 100 cubic inches, is as follows upon an average, it varies from 16 to 20, though we have occasionally found it vary from 7 to 77 cubic inches. Though our ob servations upon this point are but scanty com pared with those we made on the vital capa city, yet from about 80 experiments we con clude that man in a perfectly quiet state, as when sitting, reading, &c., breathes much less than he does under the ordinary excitement of moving about. We think the perfectly quiet breathing, when we can scarcely perceive any movement (which is by no means uncommon), may be from 7 to 12 cubic inches, and when under ordinary excitement and exercise, from 16 to 20 cubic inches ; we have known it in one case as high as 77 cubic inches. It is probable that the quantity is relative to the volume of blood to be aerated. Herbert found that adults of smaller stature breathed less than those who were taller.* It is proba ble that phthisical patients breathe very little, from 2 to 4 cubic inches; but the number of their breathing movements is greater, which compensates for this small quantity.
(d) Complemental volume. Davy, from a single experiment (upon himself), calcu lates this at 119 cubic inches t ; Kite, at nearly 200 cubic inches.t It is regulated by the position of the ordinary breathing movement, which is intermediate between it and the reserve air. It averages, from direct experiment, rather higher than the reserve volume, about 105 or 110 cubic inches. Taking the mean height at 5 ft. 8 in. the vital capacity is 230 cubic inches, that is to say (e) Vital capacity volume. Jurin and
Hales correspond in stating this at 220 cubic inches §; Davy at 213 cubic inches ; and he remarks in a note, " this capacity is pro bably below the medium. My chest is nar row, measuring in circumference but 29 inches, and my neck rather long and slender." It is probable the figures 29 are a misprint for 2 feet 9 inches round the chest. Dr. Thomson, from the mean of twelve experi ments, upon men from fourteen to thirty three years of age, states it at 1861 cubic inches. Dr. Thomson himself could expel 193 cubic inches. He mentions that this volume is constant when once determined.
The temperature of the respired air is not mentioned.* Goodwyn states it at 200 cubic inchest ; Kite, at 300 cubic inchesl ; Menzies at 200 §; Bostock II, corroborated by Dun omitting the complemental volume, at 210 cubic inches ; lastly, Thackral, who takes this volume as the measure of health ; ex amines some soldiers, who give the mean of 217 cubic inches, and some shoemakers, who average 182 cubic inches ; and he re marks, "a tall young cornet threw out 295 cubic inches ; this was the greatest quantity I ever witnessed."** According to this evidence, the respective volumes are, Cub. in.
Residual volume, from 40 to 260 Reserve JP 77 170 Breathing 3 100 ,Complemental 119 200 Vital Capacity ,, 100 300 The apparent discrepancies of the breathing volumes are entirely due to the want of col lateral observations ; for there is no distinction between the sexes, nor age, nor stature, nor weight. We have determined the vital capa city in one man as 80 cubic inches, in another 464 cubic inches ; therefore we might say this volume varies from 80 to 460 cubic inches ; but this discrepancy is cleared up, when we add that the height of the former was 3 feet 9 inches, and his weight 4 stone 9 lbs., while the latter measured 7 feet, with a weight of 22 stone ; and that if we arithmetically reduce the one to the other, the vital capa city of a dwarf is within half an inch of what it actually was, viz. 79'56 cubic inches by cal culation, and 80 cubic inches by direct expe riment. Collateral observations clear up the experiment ; thus Kite was probably a tall man, and therefore he states the vital capacity as 300 cubic inches ; Davy at 213 cubic inches, because he was of shorter stature, probably about 5 feet 7 inches ; Hales, Jurin, and Goodwyn about 5 feet 8 inches. We come to this conclusion, because we find this vo lume bear a strict relation to stature. There fore, probably, all the observations already mentioned are correct, and only wanted an other combination to remove the apparent discrepancies.
We have especially directed our attention to one of these volumes of air, the vital capacity.