142 . ANIMAL PHYSIOLOGY. 



capacity increases according to the weight in persons of 

 less than 11|- stones, and in persons above that weight is 

 jsaid to diminish at the rate of a cubic inch per pound; it 

 increases also with age up to the period from the thirtieth to 

 the thirty-fifth year, then diminishes 1^ inches every year ; 

 and it increases regularly with the height of the individual. 

 This increase of vital capacity according to height is all the 

 more interesting, as it was contrary to the expectation of the 

 observer who first noted it (Hutchinson) ; because, as he 

 justly observed, height depends principally on length of 

 limb, and he could not see how that could affect respiration. 

 The student, however, will observe that length of limb gives 

 increase of surface exposed to contact with the atmosphere, 

 and liable to be cooled thereby, and that the person who has 

 the greatest amount of surface requires the greatest amount 

 of combustion in his tissues to keep up the temperature of 

 the body, and consequently requires more oxygen, and gives 

 off more carbonic acid than others. 



It has been recently shown that a distinct influence is 

 exerted by climate on the vital capacity; it being found that 

 in the course of a voyage, the capacity, being measured in 

 the north and south temperate zones, and in crossing the 

 equator, rises in the tropics and falls again on reaching 

 temperate latitudes. This curious phenomenon apparently 

 depends on the lungs containing less blood and a greater 

 volume of air in hot climates, so that they are more compres- 

 sible in expiration. It is an accompaniment not of increased 

 but of diminished respiration (Rattray). 



The advantage of a large chest may be easily understood; 

 for the activity of respiration corresponds with the vital 

 capacity, and not with the thoracic dimensions; it is regu- 

 lated by conditions throughout the body, and not by the size 

 of the organ; therefore the smaller the lungs the greater the 

 work thrown on each portion of them, and the greatest work 

 of all is thrown on each portion when small lungs are com- 

 bined with great height. Drill masters are right in teaching 

 that an erect figure is good for the lungs; for the ribs are so 

 attached to the vertebral column, that when the column is 

 bent forwards their elevation is prevented; and that the full 

 expansion of the chest requires a straight back may be easily 



