ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



91 



Auscultation. The respiratory and cardiac sounds can be heard by 

 placing the ear against the chest, or by means of the wooden or binaural 

 stethoscope. Listen over the trachea, or at the level of the 7th 

 cervical spine. The harsh blowing inspiratory and expiratory sounds 

 are separated by an interval. These ' bronchial sounds ' are produced 

 by the vibration of the orifices of the air- way and vocal cords. 



Another breezy sound, the 'vesicular murmur,' is heard wherever 

 the lung is in contact with the chest wall. It increases during 

 inspiration and dies away during the first third of expiration. This 

 sound is probably produced by the separation of the moist surfaces 

 of the bronchioles and alveoli. It may be 

 due to the conduction of the bronchial sounds 

 to the alveoli. 



Carbonic Acid in Expired Air. Two flasks 

 are arranged as in Fig. 89 A and lime water is 

 placed in both. Breathe through the mouth- 

 piece. The inspired air passes through 

 A, which remains clear, while the expired FIG. 89A. Arrangement for 



,, i T> i i i_ -U-J demonstrating CO 2 in expired 



air passes through J3, Which becomes turbid, air by means of lime water. 



If the precipitate of calcium carbonate in B 



be collected, and a little hydrochloric acid added to it, effervescence 



will take place owing to the decomposition of the calcium carbonate. 



Deficiency of Oxygen in Expired Air. A large bottle is inverted over 

 a basin of water. A bent tube passes under the water and into the 

 bottle. Breathe in and out of the bottle through this tube. Then lift 

 up the bottle and put a lighted taper into it. The taper immediately 

 goes out. A flame will not burn in air that contains less than 17 per 

 cent. 2 ; a man can live in 10 per cent. O 2 . A flame is therefore a 

 safe test for deoxygenated air (choke damp) in wells and mines, etc. 

 The deoxygenation of the air is due to the oxidation of iron pyrites, 

 FeS 2 , etc., in the soil. A well becomes filled with such air when the 

 barometer falls. The foul air may be removed by raising and lowering 

 an open umbrella. 



An apparatus is made by Messrs. Siebe and Gorman for exploring 

 mines, wells, etc., which contain foul air. It consists of a mask, an air- 

 bag fitted with inspiratory and expiratory valves and containing potash 

 to absorb C0 2 , an oxygen bottle to supply oxygen to the bag. 



For the demonstration of the respiratory movements, gases, and 

 exchange, see pages 136 et seq. 



