190 HAND-BOOK OF PHYSIOLOGY. 



this subject is derived, that at a temperature of 60 F., 225 cubic inches 

 is the average vital or respiratory capacity of a healthy person, five feet 

 seven inches in height 



Circumstances affecting the amount of respiratory capacity. For 

 every inch of height above this standard the capacity is" increased, on an 

 average, by eight cubic inches; and for every inch below, it is diminished 

 by the same amount. 



The influence of weight on the capacity of respiration is less manifest 

 and considerable than that of height; and it is difficult to arrive at any 

 definite conclusions on this point, because the natural average weight of 

 a healthy man in relation to stature has not yet been determined. As a 

 general statement, however, it may be said that the capacity of respiration 

 is not affected by weights under 161 pounds, or 11|- stones; but that, 

 above this point, it is diminished at the rate of one cubic inch for every 

 additional pound up to 196 pounds, or 14 stones. 



By age, the capacity appears to be increased from about the fifteenth 

 to the thirty-fifth year, at the rate of five cubic inches per year; from 

 thirty-five to sixty-five it diminishes at the rate of about one and a half 

 cubic inch per year; so that the capacity of respiration of a man of sixty 

 years old would be about 30 cubic inches less than that of a man forty 

 years old, of the same height and weight. (John Hutchinson.) 



Number of Respirations, and Relation to the Pulse. The 



number of respirations in a healthy adult person usually ranges from 

 fourteen to eighteen per minute. It is greater in infancy and childhood. 

 It varies also much according to different circumstances,. such as exercise 

 or rest, health, or disease, etc. Variations in the number of respirations 

 correspond ordinarily with similar variations in the pulsations of the 

 heart. In health the proportion is about 1 to 4, or 1 to 5, and when the 

 rapidity of the heart's action is increased, that of the chest movement 

 is commonly increased also; but not in every case in equal proportion. 

 It happens occasionally in disease, especially of the lungs or air-passages, 



Vthat the number of respiratory acts increases in quicker proportion than 

 the beats of the pulse; and, in other affections, much more commonly, 

 that the number of the pulses is greater in proportion than that of the 

 respirations. 



There can be no doubt that the number of respirations of any given 

 animal is largely affected by its size. Thus, comparing animals of the 

 same kind, in a tiger (lying quietly) the number of respirations was 20 per 

 minute, while in a small leopard (lying quietly) the number was 30. In 

 a small monkey 40 per minute; in a large baboon, 20. 



The rapid, panting respiration of mice, even when quite still, is 

 familiar, and contrasts strongly with the slow breathing of a large animal 

 such as the elephant (eight or nine times per minute). These facts may 

 be explained as follows: The heat-producing power of any given animal 

 depends largely on its bulk, while its loss of heat depends to a great 

 extent upon the surface area of its body. If of two animals of similar 

 shape, one be ten times as long as the other, the area of the large animal 



