250 



EXPERIMENTAL PHYSIOLOGY. 



2. Changes in Expired Air. 



(a.) Black's Experiment. Place equal quantities of lime- 

 water in two vessels (A and B). Take a deep breath, 

 close the nostrils, and expire through a bent glass tube 

 into A. The lime-water soon becomes milky, owing to the 

 large amount of carbonic acid expired, combining with the 

 lime to form carbonate of lime. With the elastic pump of a 

 spray-producer, pump the air of the room through B. B 

 remains clear and does not become turbid. Therefore, the 

 carbonic acid must have been added to the inspired air in 

 the respiratory organs. 



(b.) Miiller's Valves. Arrange two flasks (A and B) and 

 tubes as in Fig. 115, with some lime-water in both. Close 



Fig. HS.-Muller's Valves. 



the nostrils, apply the mouth to the tube, and inspire. 

 The air passes in through A, and is freed of any C0 it may 

 contain. Expire, and the air goes out through B, in which 

 the lime-water becomes turbid. 



(c.) Heywood's Experiment. Place about two litres of 

 water in a basin, and in it put erect a bell-jar without a 

 bottom. Ascertain that a lighted taper burns in the jar. 

 Renew the air, place in the neck of the latter a glass tube 

 with a piece of india-rubber tubing attached. Close the 

 nostrils, apply the mouth to the tube, and inspire. The 

 water rises in the bell-jar. Then expire, the water sinks, 

 and the air which was originally present above the water 

 has been taken into and expelled again from the respira- 

 tory passages. Remove the cork, and place a lighted taper 

 m the expired air. The taper is extinguished (Fig. 116). 



