Expert: Walter Hintz - 9/12/2008

Question
i grew two agar dishes. one with dog saliva and the other with mine.I put them in the attic and they came out just fine. How do You count the colonies to find out the results?

Answer
I assume there are a lot of colonies.  If so here is what you do.  Using a ruler Make a grid of squares each about 1 square mm. Determine the area of the bottom of the petri dish.  Place the grid under the dish and counnt the colonies in ten random squares and find the average per square,  Now you know thw number in a single square.  Since you have determined the total area in sguare mm. All you have to do is multiply,  Rather in drawing the sguares you get some graph paper