NUMBER OF RESPIRATIONS. 



167 



forcibly expelled from the chest after the deepest possible inspiration. It is equal 

 to 3772 c.c. (or 230 cubic inches) for an Englishman {Hutchinson), and 3222 for a 

 German (Haeser). 



Hence, after every quiet inspiration, both lungs contain (1 + 2 + 3) = 3000 to 

 3900 c.cm. [220 cubic inches]; after a quiet expiration (1 + 2) = 2500 to 3400 

 c.cm. [200 cubic inches]. So that about \ to i of the air in the lungs is subject to 

 renewal at each ordinary respiration. 



Donders calculated that the entire bronchial system and the trachea contain about 500 c.c. of 

 air. 



Estimation of Vital Capacity. This was formerly thought to be of great 

 utility, but at the present time not much importance is attached to it, nor is it 

 frequently measured in cases of disease. It is estimated by means of the spiro- 

 meter of Hutchinson (fig. 134), which consists of a graduated cylinder filled with 

 water and inverted like a gasometer over water, 

 and balanced by means of a counterpoise. Into 

 the cylinder a tube projects, and this tube is 

 connected with a mouthpiece. The person to be 

 experimented upon takes the deepest possible in- 

 spiration, closes his nostrils, and breathes forcibly 

 into the mouthpiece of the tube. After doing so 

 the tube is closed. The cylinder is raised by the 

 air forced into it, and after the water inside and 

 outside the cylinder is equalised, the height to 

 which the cylinder is raised indicates the amount 

 of air expired, or the vital or respiratory capacity. 

 In a man of average height, 5 feet 8 inches, it 

 is equal to 230 cubic inches. 



The following circumstances affect the vital capa- 

 city : 



(1) The Height. Every inch added to the height of 

 persons between 5 and 6 feet gives an increase of the 

 vital capacity = 130 c.c. [8 cubic inches.] 



(2) The Body-weight. When the body-weight exceeds 

 the normal by 7 per cent, there is a diminution of 37 

 c.c. of the vital capacity for every kilo, of increase. 



(3) Age. The vital capacity is at its maximum at 35 ; 

 there is an annual decrease of 23*4 c.c, from this age 

 onwards to 65, and backwards to 15 years of age. 



(4) Sex. It is less in women than men, and even where there is the same circumference of 

 chest, and the same height in a man and a woman, the ratio is 10 : 7. 



(5) Position and Occupation. More air is respired in the erect than in the recumbent 

 position. 



(6) Disease. Abdominal and thoracic diseases diminish it. 



109. NUMBER OF RESPIRATIONS. In the adult, the number of respira- 

 tions varies from 16 to 24 per minute, so that about 4 pulse-beats occur during each 

 respiration. The number of respirations is influenced by many conditions : 



(1) The Position of the Body. In the adult, in the horizontal position, Guy counted 13, 

 while sitting 19, while standing 22, respirations per minute. 



(2) Age. Quetelet found the mean number of respirations in 300 individuals to be : 



Fig. 134. 

 Scheme of Hutchinson's spirometer. 



Year. Respirations. 

 Oto 1, 44 



5, 26 



15 to 20, 20 



Average 



Number per 



Minute. 



(3) The State of Activity. Gorham counted in children of 2 to 4 years of age during standing 

 32, in sleep 24, respirations per minute. During bodily exertion the number of respirations 

 increases before the heart-beats. [Very slight muscular exertion suffices to increase the frequency 

 of the respirations.] 



[(4) The Temperature of the surrounding medium. The respirations become more numerous 



