NUMBER OF RESPIRATIONS. 229 



109. Number of Respirations. 



In the adult, the number of respirations 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.) The age. Quetelet found the mean number of respirations in 300 

 individuals to be : 



Year. Respirations. \ 



0-1, 44 I 



5, .26 Average Number 



15-20, 20 > per 



20-25, . . 18-7 ( Minute. 



25-30, . . 16 



30-50, . . 18-1 J 



(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 the higher the surrounding temperature, but this result only 

 occurs when the actual temperature of the blood is increased, as in fever. 



(5.) Digestion- There is a slight variation during the course of the day, the 

 increase being most marked after mid-day dinner (Vierordt). 



(6.) The will can to a certain extent modify the number and also the depth of 

 the respirations, but after a short time the impulse to respire overcomes the 

 voluntary impulse. 



(7.) The gases Of the blood have a marked effect, and so has the heat of the 

 blood in fever.] 



110. Time occupied by the Respiratory Movements. 



The time occupied in the various phases of a respiration can only be 

 accurately ascertained by obtaining a curve or pneumatogram of the 

 respiratory movements. 



Methods. Vierordt and C. Ludwig transferred the movements of a part of the 

 chest-wall to a lever which inscribed its movements upon a revolving cylinder. 

 Eiegel (1873) constructed a "double stethograph" on the same principle. This 

 instrument is so arranged that one arm of the lever may be applied in connection 

 with the healthy side of a person's chest, and the other on the unsound side. 



(2.) An air-tambour, such as is used hi Brondgeest's pansphygmograph (Fig. 103, 

 A) may be used. It consists of a brass vessel, a, shaped like a small saucer. The 

 mouth of the brass vessel is covered with a double layer of caoutchouc membrane, 

 6, c, and air is forced in between the two layers until the external membrane 

 bulges outwards. This is placed on the chest, and the apparatus is fixed in posi- 

 tion by means of the bands, d, d. The cavity of the tambour communicates by 

 means of a caoutchouc tube, s, with a recording tambour which inscribes its 



