LXVI.] VITAL CAPACITY, ETC. 3II 



site side, the manubrium sterni with the third dorsal spine, the lower end of 

 the sternum with the eighth dorsal spine, and the ensiform cartilage with the 

 tenth dorsal spine." Measure oiily the first. Adjust the knob of the tambour 

 on one side against the eighth rib, as above, while the movable bar with its 

 knob is placed against the opposite corresponding rib. Connect the tambour 

 with the recording tambour, introducing a j-piece, the stem of which is 

 provided with an india-rubber bag and screw clamp to regulate the pressure 

 within the air-system. 



8. Intra-Thoracic Pressure.— For practice this can be done on a dead 

 rabbit. 



(a.) Fix the dead rabbit in Czermak's rabbit-holder. Expose the trachea, 

 tie into it a knee-shaped glass cannula. Make a small water-manometer or 

 bent U-tube with a millimetre scale attached, fill it about half full with 

 coloured water, and to the proximal limb attach an india-rubber tube with a 

 T-j)iece and screw clamp, as in other experiments. Connect the tracheal 

 cannula with the manometer tube, tighten the screw clam]), and see that the 

 water stands at the same level in both limbs of the manometer. 



(Ik) Open both pleurae without injuring the lungs. The lungs collapse and 

 the water is depressed in the proximal side of the manometer, and rises in the 

 open limb. 



9. Respiratory Movements of Frog; — In the frog the air is forced into the 

 lungs. 



(a.) Observe rhythmical movements of the muscles of the floor of the mouth 

 and of the muscles attached to the hyoid bone, the cavity of the mouth is 

 thus diminished. Coincident with these are 



{b.) ^lovements resulting in closure of the external nares, and thus the air 

 is forced into the lungs. At the same time, the glottis is opened, but the 

 mouth must be o})ened to see this. 



{c. ) The act of expiration is performed by movements of the muscles of the 

 flanks compressing the visceral contents. 



LESSON LXVI. 



VITAL CAPACITY — EXPIRED AIR — PLEURAL 

 PRESSURE— GASES OP BLOOD AND AIR. 



1. Vital Capacity. — Estimate this on Hutchinson's spirometer, 

 i.e., take the deepest possible inspiration, and then make the deepest 

 possible expiration, expiring into the mouthpiece of the spirometer. 

 The average vital capacity is about 3700 cc. (230 cubic inches), but 

 it varies with age, height, sex, and practice in using the instru- 

 ment, &c. 



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 



