MECHANICAL PHENOMENA OF RESPIRATION. 297 



we are induced to believe that contraction of the pulmonary 

 muscles takes place in man in certain morbid conditions, as 

 in some forms of asthma or of pulmonary spasms, which 

 appear to be caused, either by paralysis or spasms of these 

 muscles (the alveoli and the small bronchi). The contraction 

 of these muscular elements seems, however, to be of no great 

 importance to the normal mechanism of respiration. We 

 would not be understood to say that the muscular tissue is 

 of no service. It must not be forgotten that the elasticity of 

 the muscle forms as important a property of this tissue as its 

 contractility, and is as useful to the economy; we have 

 already seen, for instance, that the elasticity of the inter- 

 costal muscles is of more service than their contraction. The 

 muscular tissue which enters into the construction of the 

 lungs, as it appears to us, forms an elastic element, resem- 

 bling, physiologically, the elastic tissue, properly so called. 

 We need not pursue the subject farther here, having already 

 enlarged upon it, in reference to the structure of the arteries. 1 

 If the lung is an eminently elastic tissue, it must, like the 

 arteries, have a natural form to which it has a constant ten- 

 dency to return. We shall see that this is the case, and also 



the pulmonary tissue, deduced from them the following conclu- 

 sions : the pulmonary tissue is contractile in mammals and in rep- 

 tiles. This may be witnessed by means of galvanization with an 

 induced current, after having fastened the trachea, and applied 

 at the opposite extremity of the lungs two large metallic plates 

 to serve as conductors. The manometric elevation which then 

 takes place is not due to contraction of the oasophagus (as was 

 supposed by Rugenburg), for it is seen even when the lungs have 

 been extracted from Qie thorax, and when the heart and the 

 oesophagus are removed. These contractions are, however, de- 

 pendent on the pneumo-gastric nerve. It is very evident, on the 

 other hand, that this contractility is of no great physiological 

 importance; if these muscles came into play at every respiratory 

 movement, they would contract more than twenty thousand times in 

 twenty-four hours, a velocity which would entirely contradict what 

 is positively known as to the general physiology of the smooth 

 fibre. It is also plain that the contraction of the" lung is far too 

 slight to be of any service, in expiration particularly. It mav, 

 perhaps, govern some kind of peristaltic movement of the bronchi, 

 by means of which the air is mixed together (Paul Bert). Finally, 

 it is by no means an essential feature of the pulmonary parenchyma 

 and of the respiratory functions, for section of the nerves, which 

 entirely does away with it (section of the pneumo-gastric), causes 

 no derangement in the lung in this respect (P. Bert). 

 1 See p. 152, and the note on p. 154. 



