384: RESPIRATION. 



of the diaphragm as an inspirator y muscle. Carson, in 1820, 1 

 was the first to note the relation of the elasticity of the lungs 

 to the expulsion of air. Introducing a U tube partly filled 

 with water into the trachea of an animal just killed, and 

 securing it by a ligature, this observer noted a considerable 

 pressure on opening the chest ; equal in the calf, sheep, or 

 dog to a column of water of from 12 to 18 inches, and in the 

 cat or rabbit, from 6 to 10 inches. 2 



The elasticity of the lungs operates chiefly upon the dia- 

 phragm in reducing the capacity of the chest ; for the walls 

 of the thorax, by virtue of their own elasticity, have a reac- 

 tion which succeeds the movements produced by the inspi- 

 ratory muscles. A simple experiment, which we have often 

 performed in public demonstrations, illustrates the chief ex- 

 piratory influence of the elasticity of the lungs. If, in an 

 animal just killed, we open the abdomen, seize hold of the 

 vena cava as it passes through the diaphragm, and make 

 traction, we imitate the action of this muscle sufficiently to 

 produce at times an audible inspiration ; on loosing our hold, 

 we have expiration, as it is in a measure accomplished in 

 natural respiration, by virtue of the resiliency of the lungs, 

 carrying the diaphragm up into the thorax. 



Though this is the main action of the lungs themselves 

 in expiration, their relations to the walls of the thorax are 

 important. By virtue of their elasticity, they assist the pas- 

 sive collapse of the chest. When they lose this property to 

 any considerable extent, as in vesicular emphysema, they 

 offer a notable resistance to the contraction of the thorax ; so 

 much, indeed, that in old cases of this disease the movements 

 are much restricted, and the chest presents a characteristic 



1 Philosophical Transactions, 1820. 



2 If, after noting the elevation in the liquid due to the elasticity of the lungs, 

 these organs be stimulated by means of a current of galvanism, the liquid will 

 gradually rise, in obedience to the contractions of the muscular elements of the 

 bronchial tubes. This slow contraction, characteristic of the non-striated muscu- 

 lar fibres, does not intervene in the physiological phenomena of expiration, but 

 the action of these fibres i important in certain cases of disease. 



