RESPIRATION. 



343 



than the inspired air by 6'75 F. In the last 

 experiment, though the inspired air was 

 7'875 F. warmer than the internal tempera- 

 ture of the body, the expired air was only 

 about 1'125 F. warmer than what it is when 

 air of the ordinary temperature is breathed. 

 The average temperature of the expired air is, 

 according to Valentin, 99'5 F. when breath- 

 ing in an atmosphere of moderate tempera- 

 ture.* According to his calculations, when 

 a person breathes 100 cubic centimeters of 

 atmospheric air at the temperature of 60 F., 

 their bulk is increased to 1 07*87975 cubic 

 centimeters when raised to the temperature 

 of 99'5 F. in the lungs, since the expansive 

 co-efficient of atmospheric air is 0*3665. As 

 the expired air, however, contains 4'4 per 

 cent, of carbonic acid gas, and as the ex- 

 pansive co- efficient of this last gas is 0-369087 

 the expansion of the expired air will differ 

 slightly from what it would be were it com- 

 posed of oxygen and nitrogen only, and will 

 be 107-882197 cubic centimeters.f 



It is difficult to obtain an accurate estimate 

 of the quantity of watery vapour that escapes 

 from the body along with the expired air. 

 Were the inspired and expired air always fully 

 saturated with moisture, and were their quan- 

 tities, barometric pressure, and relative tem- 

 perature accurately ascertained, the absolute 

 and relative quantities of watery vapour which 

 they contain could be calculated by certain 

 algebraic formulae. The atmospheric air 

 which we breathe is sometimes saturated with 

 moisture, more frequently the dew->point, or 

 that at which the precipitation of the atmo- 

 spheric moisture can occur, is considerably 

 below the temperature of the air, and the 

 number of thermometric degrees between the 

 actual temperature of the air and the dew- 

 point shows the degree of dryness in the air, 

 or in other words how much it is below the 

 point of saturation with moisture. J The 



* Moleschott (Hollandische Beitrsige zu den 

 anatomischen und physiologischen Wissenschaften, 

 band i. heft i. S. 86. Utrecht und Pusseldorf, 

 1846) has more lately made experiments on the 

 temperature of the air in the back part of the mouth, 

 and ascertained that in a range of temperature in 

 the external air to the extent of 12-6 F. that 

 there was scarcely any difference in the temper^ 

 ature of the expired air. In 26 experiments, 

 three of which were upon women, upon indivi- 

 duals chiefly from 19 to 43 years of age, he found 

 the average temperature of the expired air to be 

 nearly 98 -6 F. The longer or shorter time which 

 the inspired air remains in the lungs will modify the 

 results in such experiments. 



t Opus cit. 



j According to the calculations made by the late 

 Professor Daniell (Elements of Meteorology, vol. ii. 

 p. 316. London, 1845) from meteorological tables, 

 kept for 17 years consecutively, the mean temper- 

 ature of London is 49--54 F., while the mean dew- 

 point is 44 0- 31, giving 5-59 upon the thermometric 

 scale, and 827 upon the hygrometric scale, as the 

 degree of dryness. The mean elastic force of this 

 watery vapour is, he says, "342 of an inch of mercury, 

 and a cubic foot contains 3-806 grains of moisture. 

 The greatest degree of dryness was 49 F., or the 

 least degree of moisture when the hygrometric scale 

 was 235. According to Dalton's observations (Man- 

 chester Memoirs, 2nd series, vol. ii.) the medium of 



loss of watery vapour by the lungs will evi- 

 dently be regulated by the temperature of the 

 inspired air, the quantity of watery vapour it 

 holds in solution, the volume of air inspired, 

 and the length of time it remains in the lungs. 

 The lower the temperature of the inspired 

 air, the less it approaches to the point of sa- 

 turation with moisture, and the greater its 

 volume, the greater will be the loss of watery 

 vapour by the lungs. When the respirations 

 are more rapid, and the sojourn of the air 

 within the lungs is short, the same volume of 

 expired air will probably contain less water in 

 solution, than when its sojourn there is more 

 prolonged, but the more frequent renewal of 

 the air within the lungs will be more than 

 sufficient to compensate for this. 



The most correct and trust-worthy expe- 

 riments to ascertain by the direct method the 

 quantity of watery vapour in the expired air 

 are those of Valentin and Brunner.* These 

 experiments were performed upon seven males 

 between the ages of 17J- and 33 years, and 

 the maximum of watery "vapour exhaled was 

 13156*323 Troy grains in the 24 hours; the 

 minimum 4511-374 grains, and the average 

 7819-222 grains. The quantity of watery 

 vapour in the expired air within a given time 

 varied in the same individual ; and in one 

 experiment it was increased after drinking. 

 In these experiments the entire quantity of 

 water in the expired air was ascertained, so 

 that the actual quantity given, off by the fluids 

 of the body must have been, less than this ; 

 and Valentin calculates that if a person 

 breathes atmospheric air saturated with 

 moisture, at the temperature of 60 Fahr., and 

 if the expired air be at the temperature of 

 99'5 Fahr. 3 and also saturated with moisture, 

 about f of the watery vapour contained 

 in the expired air will be furnished by the 

 fluids of the body.f We have seen that 



aqueous vapour in this climate (that of Manches-r 

 ter) may be estimated at '30 of an inch of mercury 

 due to the temperature of 44 F. This vapour, he 

 says, is increased by the temperature of 98 in the 

 lungs from '30 to 1*74 inch of mercury, being an 

 increase of 1*44 inch ; but it \vilj_ only be equal in 

 weight to air of 1 inch of force,, as the specific 

 gravity of vapour is less than that of air in the pro- 

 portion of 7 to 10. Valentin calculates (Opus cit. 

 p. 533) that 100 cubic centimeters of dry air under a 

 barometric pressure of 29*922 English inches, raised 

 to the temperature of 99*5 F., and saturated with 

 moisture, would be expanded to 106-488 cubic centi* 

 metres. 



* Opus cit. p. 536. Lavoisier has given different 

 estimates of the quantity of watery vapour in the 

 expired air in his papers on respiration and trans- 

 piration in the Memoires de 1'Acade'mie des Sciences. 

 Hales, Menzies, and Abernethy, from experiments 

 on themselves, and employing different kinds of ap- 

 paratus, all more or less imperfectly suited for the 

 purpose, have respectively estimated it at 9792 grs. 

 or about 20 oz., 2880 grs. or about 6 oz., 4320 grs. or 

 about 9 oz. Dalton and Thomson, from calculations 

 based upon the relative quantities of watery vapour 

 required to saturate the inspired and expired air, 

 have estimated it respectively at 1-55 or nearly llb. 

 Troy or 8640 grs., and at 19 oz. 



f Opus cit. p. 533. Vierordt (Physiologic des Ath- 

 mens, &c. S. 155. 1845) calculates from the quantity 



z 4 



