184 



APPLIED PHYSIOLOGY 



the circulation through the lung facilitated; during 

 expiration, on the other hand, the pulmonary circulation 

 is much more difficult (Fig. 9). This is one reason 

 why a patient whose circulation is embarrassed tends 



FIG. 9. 



These diagrams represent an infundibulum, A at the end of a complete 

 inspiration, and , at the end of a complete expiration, b = alveolar 

 wall ; a = bloodvessels of the same. It will be seen that the amount 

 of blood in the lungs varies directly with the amount of air, and that 

 the pulmonary bloodvessels are most dilated and the resistance to the 

 right heart least at the end of a full inspiration ; while, contrariwise, 

 the vessels are most contracted and the resistance to the right heart 

 greatest at the end of a complete expiration. (Harry Campbell.) 



instinctively to keep his chest as much as possible in 

 the position of inspiration. 



The absence of a vasoconstrictor supply to the pul- 

 monary arteries also implies that suprarenal extract 



