112 THE HUMAN MOTOR 



city." ( l ) For a healthy adult man, the vital capacity is 3-75 

 litres and 2-75 litres for a woman. ( 2 ) As a rule, from the age of 

 3 years, when it is 0400 litres, it has an annual increase of 042 

 litres. This continues up to the thirtieth year. It also increases 

 by 0-05 01 0-04 litres per centimetre increase of stature in man 

 and woman respectively ( 8 ) from 4 years ot age. In the case 

 ot macrosoles, or brachysoles, it depends on the thoracic perimeter. 



The vital capacity, as also the thoracic co-efficient, are sensibly 

 larger in persons ot medium height, and these otten appear more 

 robust and muscular than tall persons. It would even seem that 

 evolution tends to reduce the stature and give- it a more accen- 

 tuated strength and robustness. ( 4 ) Measurements of vital capa- 

 city-are therefoie very useful (see 240). 



80. (iii) Surface and Volume of the Body. The relation be- 

 tween the volume, the weight, and the density of a body is : 



If we know the density D of any body, its volume can be readily 

 deduced from its weight. D is generally taken as 1-035, which 

 figure is the mean of a large number of measurements made by 



Mies.( 5 ) 



In practice the density is determined from the volume. The 

 latter can be easily found by placing the subject in a water bath 

 and measuring the volume of water displaced. 



p 



The above value for the ratio ==' i.e., 1-035 was the mean of 



59 measurements, the subjects having their lungs partially 

 inflated. 



The estimation of the measurement of the surface of a body 

 can be made theoretically. Suppose a " cube " with a volume 

 V ; the side of the cube is 3 <y/V ; the total surface, of the six 

 faces of the solid, will be 6 X ( 3 <\/V) z = 6 HA 2 - Tt is obviou s 

 that we can substitute the weight for the volume and write S 

 = K 3 y / P*. But the co-efficient K changes according to the 

 shape of the body, which is not really cubic. For man, it is 

 found that K = 12'312. The surface is therefore : 

 S = 12- 



f 1 ) Hutchinson (Trans, of the Med.-Chir. Soc., 1848). 

 () Pagliani, (Lo Sviluppo Umano per Etd,, Milan, 1879). 

 ( 8 ) Arnold, (Ueber die Athmung des Menschen., 1855) : Snepf (Gazette 

 Midicale, 1857). 



(*) L. Manouvrier, (loc. cit., p. 200). 



( 8 ) Mies (Wirchow's Archiv., vol. civil., p. 90, 1899). 



