If you look at blood itself, 55% of it is kind of salty water. That's 55% of your blood in terms of the proportion of it. 45%, which is quite a lot, is just from one cell type. If you were to increase that somehow, and then let's say it went up to 55, that is going to be a lot thicker because it's got a lot more cells in it. How would you get greater amounts of red blood cells? Well, if you are an athlete and you particularly need to carry a lot of oxygen,. Because that's what red blood cells do, carry... How to choose your prey.