RESPIRATION. 143 



demonstrated by taking in as full a breath as possible in the 

 stooping posture, and then rising and throwing the shoulders 

 back, when it will be found that an additional quantity of 

 air can be inhaled. The stooping posture renders part of the 

 lung useless, throws the work on the rest, and leaves a smaller 

 amount of residual air with which to dilute that which is 

 inhaled. 



105. The atmosphere which we breathe consists of 79 

 volumes of nitrogen with 21 of oxygen, containing in every 

 10,000 volumes four or five of carbonic acid. It further 

 contains minute quantities of accidental gaseous impurities, 

 and has constantly numbers of exceedingly small particles 

 of organic matter floating about in it, including germs of 

 different kinds of mould. The degree of moisture varies at 

 different times, but the amount which it is capable of 

 dissolving increases rapidly with rise of temperature. 



The air exhaled in expiration differs from what has been 

 breathed, in temperature, moisture, and the quantity of 

 carbonic acid and oxygen which it contains. 



The temperature of the exhaled air is approached to that 

 of the blood, varying usually from 97 to above 99F., accord- 

 ing to the rapidity of the respiration and the temperature of 

 the surrounding air. When respiration is slow, the air has 

 longer time to become assimilated in temperature to the 

 interior of the body ; and when the surrounding temperature is 

 low, a longer contact is required to approach it to blood heat. 



The air exhaled is always nearly saturated with moisture, 

 however dry it may have been'when taken in; and therefore 

 the maximum of water is removed from the body by this 

 channel during exercise in air which is cold and dry; for 

 then the respiration is active, and the air admitted and 

 warmed within the chest requires most moisture for its 

 saturation. The average amount of water thus removed has 

 been calculated to be from nine ounces to more than a pound 

 in twenty-four hours. 



106. The volume of carbonic acid contained in the expired 

 air forms usually about 4J per cent, of its bulk. The propor- 

 tion is, however, variable. When respiration is rapid, the per- 

 centage of carbonic acid in each breath is diminished, while 

 the total amount exhaled in a given time is increased, When 



