RESPIRATION 185 



(which acts only on the terminals of such nerves) can be 

 of no use in checking haemorrhage from the lungs. 



In addition to the pulmonary set of vessels, each 

 lobule is provided with a branch of the bronchial artery 

 for the nourishment of its own tissues. Free anasto- 

 mosis between the pulmonary and bronchial sets occurs 

 at the edges of the alveoli, which render the latter liable 

 to become the seat of congestion, both in obstruction to 

 the return of blood through the pulmonary veins, as, for 

 example, in mitral regurgitation, and when there is a 

 damming back of blood in the venae cavae, as occurs 

 when the lungs themselves are the seat of the obstruc- 

 tion e.g., in emphysema. In both events bronchitis 

 will be apt to ensue. 



The pulmonary pleura is supplied by the bronchial 

 arteries, and the parietal pleura by the internal mammary 

 and intercostals, whilst the venous blood is carried away 

 by the azygos veins. The latter are very imperfectly 

 provided with valves, and hence when the pressure in 

 the right heart is raised the venous radicles in the pleura 

 readily become congested, and effusion (hydrothorax) 

 results. 



Unlike the pulmonary vessels, those of the pleura are 

 supplied with vasoconstrictor nerves, which renders them 

 susceptible to the action of adrenalin. Advantage has 

 been taken of this fact by Barr in the treatment of 

 pleural effusion. 



There are two sets of lymphatics in each pulmonary 

 lobule. First, a central set which accompany the branch 

 of the pulmonary artery and pass direct to the bronchial 

 glands at the root of the lung; the flow of lymph in 



