Lung and Kidney Knowledge

You see, I can do something similar with human blood. If I insert a tube like this into a vein somewhere, the blood will rise a little way up it. So I can insert a tube into any vein – not into all of them. Imagine that I have some artery, for example in my arm, into which I insert a small ampoule-like tube. The blood flows from the artery a little way into the tube, passes through it and flows in it. This tube is now also such that, depending on the person, it has either a higher or lower blood level. There are people in whom the blood rises very high in the tube, and in others it rises less. It follows, therefore, that people have different blood pressures, because that is the pressure that is exerted and that is shown in the tube. So it is not true that if the blood presses a little harder on the veins, the blood rises higher in the tube, but if it presses less hard, it rises less high.