192 THE MECHANISM OF 



there is a grave disturbance of the normal respiratory movements 

 in such cases. 



THE ACTION OF THE RESPIRATORY MUSCULATURE IN 

 NORMAL EXPIRATION 



A consideration of the evidence now at our disposal makes it 

 difficult to believe that normal expiration is merely the result of 

 an elastic recoil. The recoil is evidently under muscular control. 

 The antagonist of the diaphragm is the musculature of the belly 

 wall ; it is difficult to believe that the replacement of the dia- 

 phragm and the abdominal viscera at the end of an inspiration 

 is merely an elastic recoil of the abdominal musculature. One 

 cannot deduce the elasticity of a living muscle from the study of 

 the dead, but I may put on record here the following observation. 

 A piece of the human rectus abdo minis 135 mm. long stretched 

 to 180 mm. when a weight of 10 kilos was attached to it ; on 

 removing the weight it had retracted in five minutes to 150 mm. 

 It is improbable that the muscles which are attached to the ribs 

 are carried by the ribs as passive burdens during expiration. The 

 reflex co-ordination which Sherrington has shown to exist between 

 so many antagonistic groups of muscles, probably holds true also 

 for the inspiratory and expiratory groups of muscles. Duchenne 

 found that the abdominal musculature was brought into action 

 when the phrenic nerve is stimulated. Spina and Mislawsky 

 observed that stimulation of the apparent fibres in the phrenic 

 had an inhibitory action on the abdominal musculature. Baglioni 

 obtained an expiratory movement of the body .wall when the dia- 

 phragm itself was stimulated. At least one can feel the upper part 

 of the rectus abdominis harden under the fingers during expiration, 

 as if it were in action. The observation of Treves, the Italian physio- 

 logist, also points to expiration being a muscular act. He found 

 that if an inspiration is arrested, it is followed by an expiration of 

 normal amount. Mosso observed that the respiratory movement 

 became thoracic in type when the horizontal position was 

 assumed, a result which cannot be ascribed to an alteration in 

 the elastic recoil of the lung. Mosso concluded that the assump- 

 tion of the thoracic type of respiration in the supine position is 

 brought about through a reflex action of the vagus, but in the 

 writer's opinion the change is due to an alteration in the 



