RESPIRATION. 397 



The blood-pressure in the pulmonary artery is about one-third 

 to one-seventh that in the aorta. 



As to the vasomotor nerves of the lungs, we do not know whether 

 they have a tonus, or under what circumstances they are called into 

 activity. It is natural to conclude, since pulmonary vasomotor 

 nerves exist, that they are excited when the left heart has difficulty 

 in emptying itself; in this case they could contract and diminish the 

 afflux of blood to the left side of the heart. 



Pathological Action. The lungs are sixty times larger in surface 

 area than that of the body; hence the blood oxidation should be 

 perfect. 



Inspiration opens the alveolar capillaries and the circulation of 

 blood in them is accelerated. In mitral regurgitation there is a con- 

 gestion of the blood-vessels in the alveoli. 



The blood and lymph flow in the apices of the lungs are not much 

 accelerated by inspiration, for there is a much less variation in respira- 

 tory pressure. The seat of tuberculosis is for this reason often in the 

 apex of the lung. 



Keflex contraction of the bronchioles resulting in asthma may 

 be caused by polyps in the nose or by irritation from the stomach. 



Corsets by interfering with the function of the abdominal mus- 

 cles in the support of the liver and other abdominal viscera cause 

 them to be dislocated downward (Glenard's disease). 



The respiratory and vomiting centers are near neighbors in the 

 medulla oblongata; hence dyspnoea by irritating the respiratory 

 centers spreads impulses to the vomiting center. 



The excessive use of tobacco, by depressing the respiratory center, 

 may cause sighing respiration. 



