EFFECTS OF KESPIRATION ON THE AIR. 385 



1. Jh'xidualAir; that which cannot be displaced by the most powerful 

 expiration, which always remains in the thorax so long as the lungs retain 

 their natural structure, and over which, therefore, we have no control. 



2. Supplemental Air; that portion which remains in the chest after the 

 ordinary gentle expiration, but which may be displaced at will. 



3. Breathing or Tidal Air; that volume which is displaced by the con- 

 stant gentle inspiration and expiration. 



4. Complemental Air; the quantity which can be inhaled by the deepest 

 possible inspiration, over and above that which is introduced in ordinary 

 breathing. The amount which can be expelled by the most forcible expira- 

 tion after the fullest inspiration, and which is consequently the sum of the 

 2d, 3d, and 4th of these quantities, is designated by Dr. Hutchinson 1 as the 

 Vital Capacity, being that volume of air which can be displaced by II rim/ 



movement*. This "vital capacity" is less dependent than might have been 

 supposed, upon the absolute dimensions of the thoracic cavity, being yet more 

 influenced by its mobility. Thus of two sets of men of the same height, one 

 measuring 35 inches round the chest, and the other 38 inches, the average 

 vital capacity of the first was found to be 235 inches, and that of the second 

 only 226 inches ; for notwithstanding the greater absolute capacity indicated 

 by the larger circumference of the latter, the inferior mobility of the chest 

 caused more "residual air" to remain behind after the deepest expiration. 

 By taking the average of nearly 5000 observations, Dr. Hutchiuson has 

 arrived at the very remarkable conclusion, 2 that of all the elements whose 

 variation might be supposed to affect the " vital capacity," Height alone 

 seems to have any constant relation to it ; and that this relation is capable 

 of being expressed in a simple numerical form. It may be briefly expressed 

 by the rule, that for every inch of stature, from five to six feet, eight additional 

 cubic, inches of air (60 Fahr.) are given out by a forced expiration, after a full 

 inxjtiration: the vital capacity for a man from 5 feet to 5 feet 1 inch, being 

 174 cub. in. ; from 5 feet 1 inch to 5 feet 2 inches, 182 cub. in., and so on. 3 

 There is also a relation between "vital capacity" and Weight; but of a dif- 

 ferent kind from that which might have been anticipated. So far as the 

 increase in weight is simply proportional to the increase in height, the rela- 

 tion is of course the same for the one as for the other. But if the excess of 

 weight should depend upon corpulence, the vital capacity decreases in a very 

 marked manner, being always very low in corpulent men. The general re- 

 sult of Dr. Hutchinson's observations on this point, is expressed by him as 

 follows : When the man exceeds the average weight (at each height) by 7 

 per cent., the vital capacity decreases 1 cub. in. per Ib. for the next 35 Ibs. above 

 tins weight. The influence of Age upon the " vital capacity" is less marked 

 than might have been anticipated. The general fact seems to be, that the 

 "vital capacity" undergoes a slight increase between fifteen and thirty-five 

 years, and then gradually decreases, the decline being more rapid than the 

 augmentation, so that by the age of sixty-six it has diminished to about f ths 

 of the maximum. There does not seem to be as close a relation between the 

 " vital capacity" and Muscular Vigor, as might a priori have been expected, 

 and as an attempt has been made to establish. 4 Cases are not unfrequent in 

 which men of athletic constitution have an absolute deficiency, whilst others 

 by no means remarkable for physical power present a large excess. 5 In fact, 



1 Cyclop, of Anat. and Physiol., vol. iv, Art. Thorax. 



2 Op. cit., p. 1072. 



3 For similar results obtained by an ingenious method suggested by M. Grehant 

 see Med.-Chir.'Kev., Eeport on Physiology, .Jan. 1865, p. 231. 



4 See Dr. Jackson in American Medical Examiner, 1851, p. 51. 



8 See D. C. lladclyfte Hall in Trans, of Prov. Med. and Surg. Assoc., 1851. 



