PECULIARITIES IN BLOOD SUPPLY IN CERTAIN VISCERA 269 



timately on changes in aortic blood pressure; for example, an increase 

 of fifty per cent in aortic pressure may cause the coronary flow to in- 

 crease three times. The tone of the vessels also becomes lowered when 

 more blood supply is required and this dilatation is probably effected 

 by an increase in Cw of the blood (due to acid metabolic products) and 

 possibly by the appearance in the blood of substances like histamine 

 that cause dilatation of the capillaries. It is computed that the blood- 

 flow through the heart of a man during rest is 140 c.c. per minute ; during 

 muscular exercise the flow may increase to 800 c.c. Under these condi- 

 tions the oxygen consumption of the heart is increased in greater pro- 

 portion than the increase of bloodflow, which indicates that the 2 must 

 be more thoroughly utilized, i.e., the coefficient utilization becomes 

 greater (page 410). 



