312 



PRACTICAL PHYSIOLOGY. 



[LXVi. 



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.) Muller's Valves. Arrange two flasks (A and B) and tubes as in fig. 235 

 with some lime-water in both. Close the nostrils, apply the mouth to the 

 tube, and inspire. The air passes in through A, and is freed of any C0. 2 it 



may contain. Expire, and the air 

 goes out through B, in which the 

 lime-water becomes turbid. 



(c.) Hey wood's Experiment. 

 Place about two litres of water 

 in a basin, and in it put erect 

 a bell - jar. Ascertain that a 

 lighted taper burns in the jar 

 Renew the air, place in the neck 

 of the jar 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 respiratory passages. Remove the cork, and place 

 a lighted taper in the expired air. The taper is extinguished (fig. 236). 



3. Swallowing. Test on yourself how rapidly (few seconds) 

 you can swallow a large glass of water. In swallowing liquids, the 

 liquid is projected through the pharynx and oesophagus right into 

 the stomach chiefly by the contraction of the mylohyoid muscles in 

 the floor of the mouth (Kronecker and Meltzer}. 



FIG. 235. Muller's Valves. 



ADDITIONAL EXERCISES. 



4. Pressure \vithin the Pleura. Fix one end of a caoutchouc tube to a 

 water-manometer (water coloured red), and the other end to a trocar and 

 cannula. Thrust the trocar obliquely through an intercostal space until the 

 point of the trocar lies in the space between the two layers of the pleura. 

 Observe how the level of the water rises in the proximal limb of the mano- 

 meter, indicating the negative pressure in the pleural cavity. 



5. Blood Gases. Blood yields about sixty volumes per cent, of gases to a 

 vacuum. The gases in the blood C0 2 , 0, and N are extracted from it by 

 means of a gas-pump. Various forms have been constructed, including those 

 of Ludwig, Pfliiger, and Alvergniat. Study these various forms and the 

 principle ot their construction. It requires a considerable amount of time to 

 become thoroughly acquainted with the practical working of these instruments 

 but this is not necessary from a student's point of view. 



