PRACTICAL EXERCISES 



303 



(6) Expose the sciatic. Pass ice-water through the tubes, and while 

 a respiratory tracing is being taken stimulate its central end with in- 

 duction shocks so weak as just to cause an effect. Pass water at air 

 temperature through the tubes, and repeat the stimulation with the 

 coils at the same distance. Do the same while hot water is being passed 

 through the tubes, and compare the results. Always allow the water 

 to pass for a time before making an observation. 



5. Measurement of Volume of Air inspired or expired Vital Capacity. 

 A spirometer (Fig. 114, p. 235) of sufficient accuracy for this experi- 

 ment can be made by removing the bottom of a large bottle with a 

 capacity of not less than 4 litres. A good cork, through which passes 

 a glass tube connected with a rubber tube, is fitted into the neck. The 

 bottle is fixed vertically, mouth downwards, the glass tube being closed 

 for the time, and graduated, by pouring in measured quantities of water, 

 say 100 c.c. at a time, and marking the level. The divisions are then 

 etched in. If the cork does not fit air-tight, it is covered with wax. 

 The bottle is swung on two pulleys, counterpoised and immersed, 

 bottom down, in a large 

 glass jar or a small cask 

 nearly full of water. A 

 smaller bottle may be used 

 for the determination of the 

 tidal air, so as to reduce the 

 error of reading. 



(i) Submerge the bottle 

 to the stopper, after opening Fig. 138. Arrangement for Heating or Cooling 



the Blood in the Carotid Arteries. A, cylin- 

 drical portion of tube; B, flattened portion in 

 the groove, between which and A the artery 

 lies; C, cross-section, showing the lumen extend- 

 ing into B; D, rubber tube attached to a brass 

 tube soldered into A. The other end of A has 

 a similar brass tube soldered into it (not shown 

 in the figure). This is connected by a rubber 

 tube with a similar apparatus, on which the 

 other carotid lies. D is connected with a funnel 

 containing hot or cold water or with the outflow 

 tube, as the case may be. 



the pinchcock on the rub- 

 ber tube. Breathe into the 

 bottle, close the cock, ad- 

 just the bottle so that the 

 level of the water is the 

 same inside and outside, and 

 then read off the level. De- 

 termine the volume of air 

 expired in 



(a) A normal expiration 

 after a normal inspiration 

 (tidal air) ; 



(b) The greatest possible expiration after a normal inspiration 

 (supplemental air plus tidal air) ; 



(c) The greatest possible expiration after the greatest possible 

 inspiration (vital capacity). 



(2) Open the cock and raise the bottle till it is nearly full of air. 

 Determine the volume of air inspired in 



(a) A normal inspiration after a normal expiration (tidal air) ; 



(b) The greatest possible inspiration after a normal expiration 

 (complemental air plus tidal air) ; 



(c)- The greatest possible inspiration after the greatest possible 

 expiration (vital capacity). 



Make several observations of each quantity, and take the mean. 



(3) Count the rate of respiration for three minutes, keeping the 

 breathing as nearly normal as possible; repeat the observation; and 

 from the mean result and the amount of the tidal air calculate the 

 quantity of air taken into the lungs in twenty-four hours (pulmonary 

 ventilation). 



6. Cardio-Pneumatic Movements. Fill a U-tube with tobacco- 

 smoke. One end of the tube is placed in the nostril of a fellow-student. 



