RESPIRATION. 133 



The changes in the air affected by respiration are: 

 Loss of oxygen, to the extent of five cubic inches per 100 of air, or one in 



twenty. 

 Gain of carbonic acid, to the extent of 4.66 cubic inches per 100 of air, or 



0.93 inch in twenty. 



Increase of water-vapor and organic matter. 

 Elevation of temperature. 

 Increase, and at times decrease, of nitrogen. 

 Gain of ammonia. 



The total quantity of oxygen withdrawn from the air and consumed by the 

 body in twenty-four hours amounts to fifteen cubic feet, and can be readily 

 estimated from the amount consumed at each respiration. Assuming that 

 one cubic inch of oxygen remains in the lungs at each respiration, in one hour 

 there are consumed 1080 cubic inches, and in twenty-four hours 25,920 cubic 

 inches, or fifteen cubic feet, weighing eighteen ounces. To obtain this 

 quantity, 300 cubic feet of air are necessary. 



The quantity of oxygen consumed daily is subject to considerable vari- 

 ations. It is increased by exercise, digestion, and lowered temperature, and 

 decreased by the opposite conditions. 



The quantity of carbonic acid exhaled in twenty-four hours varies greatly. 

 If can be estimated in the same way. Assuming that an individual ex- 

 hales 0.93 + cubic inch at each respiration, in one hour there are eliminated 

 1008 cubic inches, and in twenty-four 24,192 cubic inches, or fourteen cubic 

 feet, containing seven ounces of pure carbon. 



The exhalation of carbonic acid is increased by muscular exercise, nitrog- 

 enous food, tea, coffee, and rice, age, and by muscular development; decreased 

 by a lowering of temperature, repose, gin and brandy, and a dry* condition 

 of the air. 



As there is always more oxygen consumed than carbonic acid exhaled, 

 and as oxygen unites with carbon to form an equal volume of carbonic acid, 

 it is evident that a certain quantity of oxygen disappears within the body. 

 In all probability it unites with the surplus hydrogen of the food to form 

 water. 



The amount of water vapor which passes out of the body with the expired 

 air is estimated at from one to two pounds. 



The organic matter, though slight in amount, gives the odor to the breath. 

 In a room with defective ventilation the organic matter accumulates and gives 

 rise to headache, nausea, drowsiness, etc. Long-continued breathing of 

 such air produces general ill health. It is not so much the presenc of CO 2 

 in increased amount as the presence of organic matter which necessitates 

 thorough ventilation. 



