THE RATE OF RESPIRATION. 207 



After complete expiration the tube is closed, and the increase of air within the 

 jar indicates the vital capacity, provided the water outside and that inside the 

 jar are at the same level. It is also advisable to allow the expired air to cool, 

 until it is of the temperature of the surrounding air. 



Of the factors that influence vital capacity the following are known: 



1. Stature. Every inch of additional height between 5 and 6 feet is accom- 

 panied by about 130 cu. cm. increase in the vital capacity. 



2. The volume of ike trunk is, on the average, seven times that of the vital 

 capacity. 



3. The Body-weight. An increase in weight of 7 per cent, above the normal 

 is accompanied by a diminution in the vital capacity of 37 cu. cm. for every 

 additional kilogram. 



4. Age. The vital capacity reaches its maximum at thirty-five years; from 

 this up to the sixty-fifth year, and backward to the fifteenth year, 23.4 cu. cm. 

 must be deducted for each year. 



5. Sex. Arnold found the average to be 3660 cu. cm. for men, and 2550 

 cu. cm. for women. For the same stature and chest-measurement, the relation of 

 the vital capacity of men to that of women is as 10 to 7. 



6. Social position and occupation have a decided influence on the physical 

 condition and nutrition, and hence also on the vital capacity. Arnold established 

 three classes, of which each preceding class exceeds the one following by 200 cu. cm. 

 greater vital capacity: (a) soldiers and sailors; (b) artisans, compositors, police; 

 (c) paupers, the nobility, and students. 



7. Miscellaneous. The vital capacity is greatest in the standing position, and 

 when the stomach is empty. It is diminished after great effort, and also in de- 

 bilitated conditions of the body. It is greater in advanced pregnancy than in the 

 puerperium. To a certain extent practice with a spirometer can increase the 

 vital capacity. 



THE RATE OF RESPIRATION. 



The rate of respiration varies in adults between 12, 16, and 24 in a 

 minute. Four pulse-beats on an average thus occur with every respira- 

 tion. Many factors influence the rate: 



1. The Position of the Body. In adults Guy noted 13 respirations 

 to the minute in the recumbent posture, 19 in the sitting posture, and 

 23 in the standing posture. 



2. Age. In 300 individuals Quetelet found the rate of respiration 

 to be as follows: 



Age. Respirations. Age. Respirations. 



Up to i year 44 Between 20 and 25 years 18.7 



At 5 years 26 25 and 30 years 16 



Between 15 and 20 years 20 3 and 5 years 18.1 



In the new-born the rate is between 62 and 68. 



3. Activity. In children between two and four years old, Gorham 

 counted 32 respirations to the minute in the standing posture, and 24 

 during sleep. As a result of bodily exertion the rate of respiration 

 increases before that of the heart-beat. The increase in respiratory 

 movements is incited by metabolic products furnished by the muscles 

 engaged in activity. In connection with violent muscular activity the 

 pulse-rate is increased principally by excitation of the center for the 

 cardio-accelerator nerves. 



4. Increase in the surrounding temperature, also febnle elevation c 

 the bodily temperature, will increase the rate of respiration, which may 

 even assume a dyspneic character. 



THE TIME RELATIONS OF RESPIRATORY MOVEMENTS. 

 PNEUMATOGRAPHY. 



In order to obtain information with regard to the periodic relations 

 of the various phases of the respiratory movements, it is necessary 1 



