EXTREME BREATHING CAPACITY. 405 



observations (males), it was ascertained that the volume in- 

 creases with age up to the thirtieth year, and progressively 

 decreases, with tolerable regularity, from the thirtieth to the 

 sixtieth year. 



These figures, though necessarily subject to certain indi- 

 vidual variations, may be taken as the basis for examinations 

 of the extreme breathing capacity in disease, which frequently 

 give important information. Of course, the breathing capa- 

 city is modified by any abnormal condition which interferes 

 with the mobility of the thorax, or the dilat ability of the 

 lungs. Of all diseased conditions, phthisis pulmonalis is the 

 most interesting in this connection. With regard to the 

 significance of the variations in this disease, Dr. Hutchinson 

 has arrived at the following conclusions : 



"It has been found that ten cubic inches below the due 

 quantity, i. e., 220 instead of 230 inches, need not excite 

 alarm ; but there is a point of deficiency in the breathing 

 volume at which it is difficult to say whether it is merely 

 one of those physiological differences dependent on a certain 

 irregularity in all such observations, or deficiency indicative 

 of disease. A deficiency of 16 per cent, is suspicious. A 

 man below 55 years of age breathing 193 cubic inches instead 

 of 230 cubic inches, unless he is excessively fat, is probably 

 the subject of disease. 



" In phthisis pulmonalis the deficiency may amount to 

 90 per cent., and yet life be maintained. The vital capacity 

 volume is likewise a measure of improvement. A phthisical 

 patient may improve so as to gain 40 upon 220 cubic inches." 



Herbst has shown 1 that the extreme breathing capacity 

 is diminished by obesity ; that it is proportionally less in 

 females than in males, and in children than in adults. 



Relations in Volume of the Expired to the Inspired Air. 

 A certain proportion of the inspired air is lost in respira- 

 tion, so that the air expired is always a little less in volume 



1 Loc. cit. 



