318 



RESPIRATION 



ribs are drawn downward and the abdominal cavity is compressed so that the 

 relaxed diaphragm is forced deeper into the thoracic cavity. In this way the 

 thorax is narrowed as much as possible in all directions. 



In Fig. 126 are represented according to Hasse two extreme types of 

 respiration; in A a purely diaphragmatic type, and in B a purely thoracic 

 type. In A no movement of the thoracic wall can be recognized, and the 



FIG. 126. A, a purely diaphragmatic type of respiration. B, a purely thoracic type, after 

 i, i, the profile of the body in inspiration; e, e, the same in expiration. 



anterior contour of the abdominal wall only is projected in inspiration (i). 

 In B the strong inspiratory movement of the thoracic wall forward and 

 upward is evident. Because of the passive elevation of the diaphragm the 

 anterior wall of the abdomen is at the same time drawn in; when the ribs 

 fall in expiration the anterior abdominal wall curves forward again. The 

 contour i, i, is the position of inspiration, the contour e, e, that of expiration. 



4. THE NUMBER OF RESPIRATORY MOVEMENTS 



In quiet breathing the number of respiratory movements in the adult man 

 is, on the average, 16 to 19 per minute; the extremes are about 11 and 24 

 (Quetelet). With younger persons the respiratory frequency is greater, being, 

 for example, during the first year on the average 44 (maximum 70, minimum 

 23) per minute, and during the fifth year on the average 26 per minute 

 (cf. Fig. 127). 



Various circumstances, however, serve to alter the respiratory frequency. 

 It is increased, for example, by muscular work (see below), by higher external 

 temperature, or by an elevated body temperature, and may reach a very high 

 value. 



