354 PHYSIOLOGY. 



introduces into the pulmonary apparatus about 20 cubic inches 

 of air. 



Among the numerous observers who have occupied themselves 

 with the study of the quantity of air put into circulation, Herbst and 

 Hutchinson, in particular, may be cited. The latter's spirometer is 

 the instrument which has been most frequently used to secure data 

 in experiments along this line. It represents essentially a gaso- 

 meter. It is furnished with a fixed scale and a movable indicator; 

 the latter follows the movements of the air receiver and indicates 

 them on the graduated scale. The receiver dips into a reservoir 

 filled with water and communicates with the chest of the experi- 

 menter by means of a rubber tube ending in a glass or metal funnel. 



To measure the volume of air concerned in exaggerated respira- 

 tion, the experimenter is made to stand up, care being taken that his 

 chest is free from any restraint that would hinder the mobility of his 

 chest. After several forceful inspirations and expirations, he inhales 

 the greatest quantity of air that he can draw into his lungs. With 

 the tube of the spirometer between his lips he then makes the fullest 

 possible expiration. 



By subjecting about two thousand persons to this test Hutchin- 

 son recognized that the quantity of air which a maximum inspiration 

 and expiration can put into circulation varies according to the 

 individual. It is 230 cubic inches for a man 5 feet 8 inches in 

 stature. According to this observer, the prime factor in producing 

 variance in pulmonary capacity is mainly the size of the individual. 



For every inch of height from 5 feet to 6 feet, 8 additional 

 cubic inches are given out by a forceful expiration after a full 

 inspiration. Vice versa, for every inch below the 5-foot mark the 

 capacity is diminished by the same amount. 



The mobility of the thoracic walls has here a real influence. 

 Persons with narrow chests are sometimes found who can dilate the 

 thorax much more than those in whom the circumference of that 

 part of the body is greater. With equal dimensions, the number 

 indicated by the spirometer increases with the dilatability of the 

 thorax. 



The individual's capacity appears to be greatest in the period 

 from the twenty-fifth to the fortieth year, showing a gradual 

 increase until the latter mark is reached. From this point it begins 

 to diminish, to become, in old age, less than it was even in youth. 



Observers agree in admitting that, in woman, the maximum 

 volume expired is perceptibly less than in man. The difference is 



