And during the purification process we can continually calculate the specific activity value. And if the specific activity value is increasing then what that means is our sample is getting pure and pure. And eventually if we have a sample in which we only have that enzyme, the lactate dehydrogenase, at this particular point we're going to reach a maximum value for that specific activity and this will no longer increase. The slope will be zero, it will be a straight line. So we can see that this value, which is calculated by knowing this and the concentration can be used to basically determine if our sample is in fact pure. Now, in the next lecture, we're actually going to discuss how we purify our sample by beginning with our cell.