This model, unfortunately, is plenty complicated, and involves two quantities which are very difficult to measure ( and ). One avenue of simplification is to assume that certain effects are not going to be important (for example, if one assumes that osmotic leakage is small, then essentially ). An additional simplifcation arises from the fact that equations (6 - 8) form a compartment model if , or alcohol inhibition is neglected. That is, at some level everything is accounted for, nothing lost, and therefore the derivative of some summed up quantity must be zero. To see this, set and add up (6 - 8) in the following way: