Now, as an example, let's take a section of our capillary found within our lung. And let's assume this section contains exactly one liter of blood or one liter of the red molecules. Now, a capillary is simply a very, very small vessel that carries blood. And within a capillary, oxygen and nitrogen can be exchanged with the environment. And we're using lungs because gases are exchanged within our lungs. So we want to find a number of blue molecules and a number of green molecules in terms of grounds found within one liter of this blood.