xn MECHANICS OF EESPIEATION 417 



During inspiration and quiet expiration, the anterior profile of the 

 thorax and abdomen oscillate between the limits of the boundaries 

 of the black line nn '. It will be seen that this tract is deepest in 

 man at the level of the epigastrium, and in woman at the upper 

 region of the mammae. The excursion of the thoracic-abdominal 

 profile of maximal inspiration reaches the dotted line in the two 

 figures, and in, maximal expiration it falls to the outline of the 

 same. It will be seen that during forced respiration there is no 

 longer the marked difference observed in quiet breathing, between 

 the variations of the sagittal diameter of the thorax in man and 

 woman. In both there is maximal costal dilatation and forward 

 displacement of the sternum during forced inspiration, and 

 maximal abdominal retraction in forced expiration. 



According to Hutchinson, the difference between the normal 

 types of respiration in man and woman is not the effect of stays, 

 because this type of breathing is seen in girls who have never 

 worn them. Apparently it is a secondary sexual character, formed 

 in the course of phylogenesis as the effect of pregnancy, which 

 necessarily develops costal respiration, increasing intra-abdominal 

 pressure, and confining the action of the diaphragm. Many, 

 however, hold that the thoracic type of respiration is an effect of 

 the corset or ceinture (Beau and Maissiat, Walsche, Sibson), and 

 A. D. Waller has put forward the same opinion, adducing the fact 

 that women of savage races, like the males, exhibit abdominal 

 respiration. 



As regards the abdominal type of respiration in the male sex, 

 it is desirable to correct an error that is widespread even in 

 modern text -books, to the effect that the diaphragm exerts a 

 preponderating influence over all the other inspiratory muscles. 

 A. Tick (1866) remarked that inspiratory movements can be pro- 

 duced on oneself, with a little practice, by throwing the diaphragm 

 only into action. This is most easily effected by associating the 

 idea of pressing the contents of the abdomen with the act of 

 inspiration. During this purely diaphragmatic inspiration, the 

 transverse and antero-posterior diameters of the thorax undergo 

 hardly any change, save near the base, where they are slightly 

 enlarged, although less than in normal costal breathing. 

 Fick affirms that only the sagittal diameter near the ensiform 

 process increases, and that the transverse diameter near the last 

 ribs diminishes : but we have been unable on ourselves to verify 

 this last assertion. We have always found that pure diaphragmatic 

 breathing is far more fatiguing than normal respiration, the proof 

 being that man as well as woman normally breathes more with 

 the whole of the external intercostal muscles, which elevate and 

 extend the ribs, than with the diaphragm. 



If we assume with Bonders that the external surface of the 

 thoracic cavity covers some 20 dcm., and that this surface on an 



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