COMPOSITION OF EXPIRED AIK. 



I8 7 



saturated to the extent of 70 per cent. If the air be too dry, it irritates the respiratory mucous 

 membrane ; if too moist, there is a disagreeable sensation, and if it be too warm, a feeling of 

 closeness. Hence,- it is important to see that the proper amount of watery vapour is present in 

 the air of our sitting-rooms, bedrooms, and hospital wards. 



The absolute amount of moisture varies : In towns during the day it increases with 

 increase of temperature, and diminishes when the temperature falls ; it also varies with the 

 direction of the wind, season of the year, and the height above sea-level. 



The relative amount of moisture is greatest at sunrise, least at midday ; small on high 

 mountains ; greater in winter than in summer ; larger with a south or a west wind than with a 

 north or an east wind. 



The air in midsummer contains absolutely three times as much watery vapour as in mid- 

 winter, nevertheless the air in summer is relatively drier than the air in winter. 



3. The air expands by heat. Kudberg found that 1000 volumes 

 of air, at 0, expanded to 1365 when heated to 100 C. 



4. The density of the air diminishes with increase of the height 

 above the sea-level. 



124. COMPOSITION OF EXPIRED AIR. 1. The expired air 

 contains more C0 2 in normal respiration = 4*38 vols, per cent. (3*3 

 to 5 '5 per cent.), so that it contains nearly 100 times more C0 2 

 than the atmospheric air. 



2. It contains less (4*782 vols, per cent, less) than the atmo- 

 spheric air, i.e., it contains only 16'033 vols, per cent, of O. 



3. Respiratory Quotient. Hence, during respiration, more O is 

 taken into the body from the air than C0 2 is given off ; so that the 

 volume of the expired air is (^ to -^) smaller than the volume of 

 the air inspired, both being calculated as dry, at the same tempera- 

 ture, and at the same barometric pressure. The relation of the O 

 absorbed to the C0. 2 given off is 4*38 : 4*782. This is expressed 

 by the " respiratory quotient " 



ca 



sw 



4. An excessively small quantity of N is added to the expired air 

 (Regnault and Reiset). Segen found that all the N" taken in with 

 the food did not reappear in the excreta (urine and faeces), and he 

 assumed that a small part of it was given off by the lungs. 



5. During ordinary respiration the expired air is saturated with 

 watery vapour. It is evident, therefore, that when the watery 

 vapour in the air varies, the lungs give off different quantities of 

 water from the body. The percentage of watery vapour falls during 

 rapid respiration {Moleschott). 



6. The expired air is warmer (36*3 C). It is very near the . h< ' 

 temperature of the body, and although the temperature of the sur- g " '* 

 rounding atmosphere be very variable, the temperature of the expired air still 

 remains nearly the same. 



Fig. 147 shows the instrument used by Valentin and Brunner to determine the temperature 

 of the expired air. It consists of a glass tube, A, A, with a mouthpiece, B, and in it is a line 

 thermometer, C. The operator breathes through the r nose and expires slowly through the 

 mouthpiece into the tube. 



Temperature of 

 the Air. 



-6-3 C, 

 + 17-19 C. 

 + 44 C, . 



Temperature of the 

 Expired Air. 



+ 29*8 C. 

 + 3^2-37 C. 



+ 38-5 C. 



7. The diminution of the volume of the expired air mentioned under (3) is far 

 more than compensated by the warming which the inspired air undergoes in the 



