KESPIKATION. 185 



scale placed in connection with this, the number of cubic inches is read 

 off. 



In healthy men, the respiratory capacity varies chiefly with the sta- 

 ture, weight, and age. 



It was found by Hutchmson, from whom most of our information on 

 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 respira- 

 tion is not affected by weights under 161 pounds, or 1H 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 exer- 

 cise or rest, health or disease, etc. Variations in the number of respira- 

 tions 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 move- 

 ment is commonly increased also ; but not in every case in equal propor- 

 tion. It happens occasionally in disease, especially of the lungs or 

 air-passages, that the number of respiratory acts increases in quicker pro- 

 portion than the beats of ihe 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 fa- 

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



