146 ELEMENTARY PHYSIOLOGY less. 



viscera of the abdomen upwards against the under surface 

 of the diaphragm, and so driving the floor of the thorax 

 upwards. 



It is for this reason that, whenever a violent expiratory 

 effort is made, the walls of the abdomen are obviously 

 flattened and driven towards the spine, the body being at 

 the same time bent forwards. 



In taking a deep inspiration, on the other hand, the 

 walls of the abdomen are relaxed and become convex, the 

 viscera being driven against them by the descent of the 

 diaphragm — the spine is straightened, the head thrown 

 back, and the shoulders outwards, so as to afford the 

 greatest mechanical advantiige to all the muscles which 

 can elevate the ribs. 



It is a remarkaljle circumstance that the mechanism of 

 respiration is somewhat different in the two sexes. In 

 men, the diaphragm takes the larger share in the process, 

 the upper ribs moving comparatively little ; in women, 

 the reverse is the case, the respiratory act being more 

 largely the result of the movement of the ribs. 



Si(jhi)ig is a deep and prolonged inspiration. " Sniffing " 

 is a more rapid inspiratory act, in which the mouth is kept 

 shut, and the air made to pass through the nose. 



Hiccough is the result of a sudden inspiration, due to 

 a contraction of the diaphragm, during which the glottis 

 is suddenly closed and the column of air, striking on the 

 closed glottis, gives rise to the well-known and character- 

 istic sound. 



Coughing is a violent expiratory act. A deep inspiration 

 being first taken, the glottis is closed and then burst open 

 by the violent compression of the air contained in the 

 lungs by the contraction of the ex^jiratory muscles, the 

 diaphragm being relaxed and the air driven through the 

 mouth. In sneezing, on the contrary, the cavity of the 

 mouth being shut off from the pharynx by the approxima- 

 tion of the soft palate and the base of the tongue, the air 

 •is forced through the nasal passages. 



