274 ^ MANUAL OF PHYSIOLOGY 



passing it until it has produced an effect. Then stop the drum, and 

 circulate water at the ordinary temperature till the breathing is again 

 normal. Then, while a tracing is being taken, pass ice-cold water 

 through the tubes, and again notice the effect. 



3. Measurement of Volume of Air inspired or expired. Vital 

 Capacity. A. spirometer (Fig. 79, p. 207) of sufficient accuracy for 

 this experiment 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 then 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. 



(1) Submerge the bottle to the stopper, after opening the pinch- 

 cock on the rubber tube. Breathe into the bottle, close the cock, 

 adjust the bottle so that the level of the water is the same inside and 

 outside, and then read off the level. Determine the volume of air 

 expired in : 



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



(<) The greatest possible expiration after a normal inspiration 

 (supplemental 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) ; 



() The greatest possible inspiration after a normal expiration 

 (complemental 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). 



4. Respiratory Pressure. Connect a strong rubber tube with a 

 glass bulb, and the bulb with a mercurial manometer provided with a 

 scale, (i) Fasten the tube with a little cotton-wool in one nostril, 

 breathe through the other with closed mouth, and observe the amount 

 by which the level of the mercury is altered in ordinary inspiration 

 and expiration. 



(2) Repeat the observation with forced breathing, pinching the 

 tube at the height of inspiration and expiration, and reading off the 

 maximum inspiratory and expiratory pressure. 



