THE VOLUME OF AIR BREATHED BY MAN 



39 



exercise. These determinations involve the element of consciousness, under 

 which condition it is difficult for a person to breathe with his normal rate 

 and depth. 



Make a series of determinations of respiratory rates of persons who are 

 sitting quietly but unconscious of your determinations. Count the rates 

 in a number of persons of different ages; where possible, take into considera- 

 tion height, weight, etc. Tabulate the results for a 

 comparison and for future reference. 



2. The Character of Respiratory Movements 

 in Man. A number of instruments have been de- 

 vised for measuring human respiratory movement, 

 many of which measure the change in diameter of 

 the chest in respiratory movement. Adjust one of 

 these, for example Burdon- Sanderson's stethograph, 

 to the thorax, and record the movement of the re- 

 ceiving tambour on a smoked-paper kymograph 

 which travels at the rate of i cm. per second. This 

 record, called a stethogram, will exhibit the respira- 

 tory rate, the relative time of the inspiratory and 

 expiratory phases, and the character of each. 



3. The Actual Change of Diameter in the 

 Chest in Respiration. Use a caliper provided for 

 the purpose and measure the dorso- ventral diameter 

 of the chest at a series of points along the sternum, 

 taking the reading at the height of the inspiratory 

 phase and of the expiratory phase in ordinary respi- 

 ration. Repeat the measurement in forced respira- 

 tion. Map the results on millimeter paper, as 

 indicated in figure 244. 



Repeat these measurements in the transverse 

 diameter at the first, fifth, and tenth ribs. 



Using the chest pantograph, figure 245, record 



the outline of the chest at the level of the middle of the sternum during 

 expiration and at the end of inspiration. 



4. The Volume of Air Breathed by Man. Determine the average 

 volume of air breathed per respiration, using Hutchinson's spirometer, figure 

 235, set the instrument at the zero point, exhale into the instrument through 

 the tube, using all possible care to breathe with your normal rate and depth. 

 Better results will be obtained by taking the average from sets of ten consecu- 

 tive expirations into the instrument. From the average of the volume per 

 respiration, and the average number of respirations per minute, determined 

 in Experiment i, calculate the amount of air breathed per hour and 

 per day. 



FIG. 244. Change in 

 Diameter of the Body in 

 Respiration, Costal Type. 

 a, Outline of the body in 

 forced expiration. In the 

 heavy continuous line, b, 

 the outer margin indicates 

 the contour of the body in 

 ordinary inspiration and 

 the inner margin that of 

 ordinary expiration. c, 

 Contour of forced inspira- 

 tion. (After Hutchinson.) 



