FREQ UENC Y OF RES FIR A TION IN MAN. 
747 
lungs, and other factors which bear upon the composition of the air in 
the lungs. 
The frequency of respiration in man. — Under normal conditions 
this could he readily and exactly determined, were it not liable to 
variations as soon as the attention of the subject is directed to the 
hreathing. Aim it from this, the most important causes of variations 
in the frequency of respiration are age, exercise, and temperature. 
Age. — The frequency of breathing decreases from birth to old age, 
as shown by the following table, the result of three hundred observations 
made by Quetelet l upon human subjects of the male sex. 
Age. 
RESPIRATIONS PER MINUTE. 
Maximum. 
Minimum. 
Mean. 
Xewly-born 
5 years 
15-20 ): 
20-25 ,, 
25-30 ,, 
30-50 „ 
70 
32 
24 
24 
21 
23 
23 
16 
14 
15 
11 
44 
26 
20 
18-7 
16-0 
18-1 
In healthy infants the respiration is very irregular in frequency, 
and often of the Cheyne- Stokes type. 2 
The average frequency of respiration in 1S97 adult males was found 
by Hutchinson 3 to be 20 per minute, one-third of the cases breathed 
at that rate, and 1731 between 16-24 per minute. 
Exercise increases not only the frequency but also the depth of 
breathing. This hyperpncea is not due to a deficiency of oxygen or an 
accumulation of carbon dioxide in the blood, but probably to some pro- 
duct which is derived from the metabolism in the muscles, and stimulates 
the respiratory centre. 4 
The physiological explanation of the condition, well known to athletes as 
" second wind," appears to be unknown ; during violent exercise, such as 
running or rowing, there is, after a time, considerable dyspnoea, but if the 
exercise be continued this discomfort disappears, sometimes quite suddenly; 
the man has now got his " second wind," and can continue the exertion in com- 
parative comfort. The dyspnoea in these cases appears to be partly cardiac, 
for the pulse-rate may be more than doubled, but when the " second wind " is 
obtained, there appears to be a marked decrease in the frequency of the heart's 
contraction. 5 The causes of this accommodation are unknown. 
1 "Sur l'homme et le developpement de ses facult^s," Paris, 1835. 
2 See Preyer, "Specielle Physiologie des Embryo," Leipzig, 18S5, S. 179 ; Eckerlein. 
Ztschr.f. Geburtsh. u. Gyncil:, Stuttgart, 1890. Rd. xix. S. 120. 
3 Med. -Chi r. Trans., London, vol. xxix. p. 137 ; art. "Thorax," Todd's " Cyclopaedia of 
Anat. and Physiol.," vol. iv. p. 1085. 
4 Geppert and Zuntz, Arch. f. d. gas. Physiol., Bonn. 18S8, Bd. xlii. S. 189. 
5 Result of a few observations by Penibrey and Reynolds. 
