CIRCULATION.] PHYSIOLOGY. 63I 



hepatic artery, H.A. : there it breaks up in the 

 liver into small arteries, and then into capillaries, 

 which mingle with the capillaries of the portal vein, 

 and form one system, out of which the hepatic veins 

 spring. So you see it makes a great difference to a 

 red corpuscle which is travelling along the lower part 

 of the aorta A^, whether it takes a turn into the 

 branch going to the alimentary canal, or whether 

 it goes straight on into, for instance, a branch going 

 to some part of the leg. In the latter case, having 

 got through a set of capillaries, it is soon back into 

 the vena cava and on its road to the heart. But if 

 it takes the turn to the alimentary canal, it finds after 

 it has passed through the capillaries and got into the 

 portal vein, that it has still to go through another set 

 of capillaries in the liver before it can pass through 

 the hepatic vein into the vena cava. 



This then is the course of the circulation. Right 

 side of the heart, pulmonary artery, capillaries of the 

 lungs, pulmonary vein, left side of the heart, aorta, 

 capillaries somewhere, sometimes two sets, sometinies 

 one, vena cava, right side of the heart again. A 

 little corpuscle cannot get from the right to the left !! 

 side of the heart without going through the capillaries , 

 of the lungs. It cannot get from the left side of the || 

 heart to the right without going through some capil- 

 laries somewhere in the body, and if it should happen 

 to take the turn to the stomach, it has to go through 

 two sets of capillaries instead of one. 



You see, you really have two circulations, and you || 

 have two hearts joined together into one. If you 

 were very skilful you might split the heart in half and 

 pull the two sides asunder, and then you would have 



