182 ANTHROPOLOGY. 
passages, so that this instrument gives invaluable indications as to the 
extent and nature of pulmonary disease. “ 
Physical and chemical phenomena of respiration. The tension of the 
gases in the air passages of the lungs varies according to the intensity of 
respiration. In quiet breathing, this amounts to J; or 7; of the strength with 
which the blood usually flows in the larger arteries. In feeble respiration 
the amount is not more than half of this. These values increase with any 
obstruction to respiration. The circumference of the thorax at the pit of 
the stomach in full grown men, amounts during quiet respiration to from 
31 to 1, rarely 11 of the length of the body. Hach single aspiration con- 
tinues longer than a contraction of the heart, and its duration increases 
with age. The new born infant generally respires forty-four times in a 
minute, the child of five years only twenty-six. From fifteen to twenty 
years, twenty times; from twenty to twenty-five, eighteen times; from 
twenty-five to fifty, sixteen or eighteen times. A mean act of respiration, 
therefore, in the adult lasts from three to four seconds. These values are 
of course subject to considerable variation. 7 
The air introduced into the lungs is first brought to the temperature of 
the body, whatever be the temperature of the external atmosphere. Again, 
the air in the lungs is saturated with moisture, the amount dependent upon 
the barometric pressure and the temperature. During respiration in a cool 
atmosphere, the exhaled air must contain more moisture than the atmosphere ~ 
itself. Consequently the blood loses more moisture in winter than in 
summer, this difference, however, being equated by the greater loss by 
perspiration during the latter season ; in winter again, the amount of urine 
discharged is greater. The amount of water lost depends upon the size of 
the lungs. Adult men between seventeen and thirty-five years may lose 
from + to 12 pounds in twenty-four hours. The number of aspirations does 
not seem materially to affect the result. 
The composition of atmospheric air is pretty much the same in all 
countries and during each season of the year, the variation observed being 
exceedingly slight. Recent experiments show that there are 20.81 parts 
of oxygen and 79.19 of nitrogen by volume, and 22.01 of oxygen and 76.99 
of nitrogen by weight. The amount of carbonic acid appears subject to 
decided variation, although, under ordinary circumstances, it is exceedingly 
slight. The air over the sea appears to contain less oxygen than that 
above the land and along the coast; and again, on the other hand, the air 
contained in snow is richer in this gas. According to some observers, the 
amount of oxygen in the air of high mountains and deep mines is less than 
the standard. 
A series of carefully conducted analyses of expired air shows that the 
oxygen is in much less proportion than in the atmosphere, while there is a 
large amount of carbonic acid. This carbonic acid must therefore have 
been formed in the system by the combination of oxygen with carbon of 
the blood. The amount of oxygen absorbed is about 23 per cent. The 
total amount of carbonic acid exhaled by a man within a given time may 
be expressed either by weight or volume, or by the value of the carbon. 
888 
