598 PHYSIOLOGY OF RESPIRATION. 



worn tight dress. Later observers, however (Mays, Kellogg, and 

 others), state that Indian and Chinese women who have not worn 

 tight dress exhibit the abdominal type, and the same statement is 

 made regarding civilized white women who habitually wear loose 

 clothing. It would appear, therefore, that the assumption of the 

 costal type by women in general is due to the hindrance offered by 

 the clothing to the movements of the abdomen. From an exami- 

 nation of four hundred and seven cases Fitz * concludes that when 

 the restricting effect of dress is removed there is little or no differ- 

 ence in the type of respiration in the two sexes. The natural type 

 is one in which " the movement is fairly equally balanced between 

 chest and abdomen, the abdominal being somewhat in excess." 

 When the respiration becomes dyspneic it takes on a distinctly 

 costal type, and Fitz and others have shown that for an equal in- 

 crease in girth the thoracic movements cause a greater enlargement 

 of the lungs. 



Accessory Respiratory Movements. In addition to the mus- 

 cles whose action directly enlarges or diminishes the capacity of the 

 thorax certain other muscles connected with the air passages con- 

 tract rhythmically with the inspirations, and may be designated 

 properly as accessory muscles of inspiration. The muscles es- 

 pecially concerned are those controlling the size of the glottis and 

 the opening of the external nares. At each inspiration the elevators 

 of the wings of the nose come into play. This movement occurs in 

 normal breathing in many animals, such as the rabbit and horse, 

 and in some men, while in dyspneic breathing it is invariably 

 present. The useful result of the movement is to reduce the resis- 

 tance to the inflow of air. So in many animals the glottis is dilated 

 at each inspiration by the contraction of the posterior crico-aryte- 

 noid muscles, and in man also this movement is evident when 

 the breathing is at all forced. The useful result in this case also is 

 a reduction in the resistance offered to the inflow of air. 



The Registration of the Rate and Amplitude of the Respira- 

 tory Movements. : Many methods are employed to register the 

 rate or amplitude of the respiratory movements. Upon man the 

 amplitude may be measured directly by a tape placed at different 

 levels to ascertain the increase in girth, or it may be recorded by 

 some form of lever or tambour applied to the chest or abdomen. 

 A convenient instrument for this purpose is the pneumograph 

 described by Marey, which is illustrated and described in Fig. 245. 

 In animal experimentation the various methods that are employed 

 may be classified under four heads: (1) Methods in which the 

 change in circumference or diameter of the chest or abdomen is 

 recorded. (2) Methods in which the change of pressure in the air 

 * Fitz, "Journal of Experimental Medicine/' 1, 1896. 



