310 PRACTICAL PHYSIOLOGY. [LXV. 



cannula attach an india-rubber bag such as is used with a spray- 

 producer, and inflate the Umgs. Cease to pump air into the lungs, 

 and observe how they collapse. 



3. Hydrostatic Test. 



Cut out the lungs and the heart. Place them in a vessel 

 of water. The whole will float, as the lungs contain so much air. 

 Cut ofl" a small piece of one lung, throw it into water, it floats. 

 This is the hydrostatic test. Compare a piece of pneumonic lung ; 

 the latter sinks. 



4. Apnoea. — Count the number of your own respirations per 

 minute. Take a series of rapid inspirations. Isote that several 

 seconds elapse before the next insniration. This is the period of 

 apnoea. 



Fia. 234.— Stethograph Tracing, taken with Rotlie'a Polygraph. 



5. Deglutition Apnoea. 



(a.) Test how long you can "hold your breath." Note the 

 time. 



(b.) After a time, sip water without breathing, and note that, 

 under this condition, the time the breath can be held is nearly 

 doubled. The successive acts of deglutition influence the respira- 

 tory centre in the medulla oblongata, as well as the cardio-inliibitory 

 centre {Kronecker). The latter is referred to at p. 312. Other 

 centres are influenced by sipping. 



6. Voluntary Respiration. — Test in yourself how long this can 

 be kept up. As a rule, one cannot continue it for more than two 

 minutes. 



7. Stethometer of Burdon-Sanderson. 



(a.) Prepare a drum and time-marker as in the previous experiments. 

 Cause a person to expose his chest, and seat himself conveniently. The instru- 

 ment is suspended by a broad band placed round the neck, the horizontal bar 

 being behind the body. 



(h.) The most important diameters of the chest to measure are— "Those 

 connecting the eighth rib in the axillary line with the same rib on the oppo- 



