122 Mr. Le Gros Clark on the Mechanism of Respiration. 



" Some Remarks on the Mechanism of Respiration/'' By F. Le 

 Gros Clark, Surgeon to St. Thomas's Hospital, Member of 

 Conncil and of the Conrt of Examiners of the Royal College of 

 Surgeons, and late Hunterian Professor of Surgery and Patho- 

 logy in the College, and Examiner in Surgery at the Uni- 

 versity of London. Communicated by P. Martin Duncan, 

 M.B., E.R.S., Professor of Geology in King's College, London. 

 Received April 18, 1871*. 



1 . In performing some experiments on recently slaughtered animals, 

 for the elucidation of a subject which I was then engaged in investigating, 

 I was struck with the remarkable arched tension of the diaphragm, a con- 

 dition which continued unabated until air was admitted into the pleural 

 spaces, and then it became flaccid and descended. This altered condition was 

 attended by collapse of the lungs, which receded from the thoracic walls, 

 and occupied a much smaller space than previously. 



2. In order to measure the quantity of air expelled from the lungs in 

 the preceding experiment, and to ascertain how far the collapse of the 

 lungs and the altered condition of the diaphragm were dependent on each 

 other, the following experiment was performed. The trachea of a sheep, 

 immediately after death, was exposed in the neck, divided, and tied over a 

 glass tube, which was put in communication with a graduated receiver 

 placed under water, and guarded by a stopcock. The pleurse were then 

 opened, and as air entered the diaphragm became flaccid ; but the lungs 

 remained unchanged in position and form. The stopcock was then opened, 

 and a rush of air, displacing the water in the receiver, was accompanied 

 by collapse of the lungs. The quantity of air thus forcibly expelled was 

 from ten to twelve cubic inches. 



3. The interpretation of this experiment is— 



(a) That the passive tension of the diaphragm is due to the atmo- 

 spheric pressure on its abdominal surface, which is not counterbalanced 

 by a corresponding pressure on the opposite or thoracic surface, until air 

 is admitted into the pleurse. 



(b) That the lungs retain their supplemental air by virtue of this tense 

 condition of the diaphragm, the elasticity of the former being resisted by 

 the tension of the latter. 



(c) That the contractility of the lungs, tending to the expulsion of the 

 supplemental air, removes the atmospheric pressure from the upper sur- 

 face of the diaphragm, and thus produces and maintains its arched form 

 and tense condition. 



(c?) That as soon as the pressure on the inner and outer surfaces of the 

 lungs was equalized, by the admission of air into the pleurae, their con- 

 tractility forced out the supplemental air ; and the quantity thus expelled 



. * Read May 25, 1871. See abstract, vol. xix. p. 486. 



