RESPIRATION 183 



even when one lung has been completely destroyed, or 

 rendered temporarily useless by disease, shows that a 

 much smaller alveolar area than this is sufficient to allow 

 of efficient oxidation of the blood. 



Bloodvessels, Nerves, and Lymphatics of 

 the Lung". 



Each lobule is supplied by a branch of the pulmonary 

 artery, which accompanies the bronchiole and divides 

 with it, ending by pouring its blood into the capillary 

 network in the walls of the alveoli. From the margin 

 of that network the purified blood is taken up by a branch 

 of the pulmonary vein, and ultimately returned to the 

 left auricle. The lobular branches of the pulmonary 

 artery are therefore ' end arteries,' and so liable to 

 become the seat of embolic infarction a process often 

 met with in cardiac disease. 



The balance of evidence is opposed to the view that 

 the pulmonary bloodvessels are possessed of vasomotor 

 nerves.* Hence, perhaps, the ease with which they 

 become the seat of passive engorgement when there 

 is any obstacle to the onflow of blood into the left heart, 

 and enable the lungs to act as a reservoir for the 

 pulmonary circulation in much the same way as the liver 

 serves the systemic. There can be no doubt, also, that 

 such passive congestions play a large part in the diseases 

 of the lungs. By the expansion of the lungs during 

 inspiration the alveolar capillaries are opened out and 



* See Brodie, ' The Pulmonary Circulation,' Lancet, 1902, i. 803. 



