Why do resus kits talk about doses of adrenaline in ratios instead of units?

Why do resus kits not talk about doses of adrenaline in milligrams? They state things like 1:1000 or 1:10000!

I was in A+E today and was being shown around the resus stuff. The adrenaline is in 1:10000 for example, and I couldn't workout why this was. I didn't have the courage to ask at the time.

Authored By Sally Ralton on Monday 1st October 2012