1.

Place one dime-sized piece of thymus tissue into the mortar with a small amount of sand (a pinch is sufficient). Twist the pestle twice, just enough to flatten the tissue. It's ok if it sticks to the pestle. (The grinding will break up the tissue.)

2.

Using a graduated cylinder, measure and add 4 ml of water to the mortar. Grind the substance until it appears cloudy enough to hide the grains of sand. (Grinding strips the cells down to their nuclei.) The cloudiness is from the outer parts of the cells being broken away form the nuclei.

3.

Pour only the liquid from the mortar into the test tube–you do not need every last drop. Wipe out the mortar and pestle with a paper towel and put it into the trash. (This separates the cell nuclei from the outer pieces, which are left behind with the sand.)

4.

Add three drops of liquid dish soap to the test tube. Mix well to dissolve the dish soap. Use your thumb to hit the bottom of the test tube rhythmically, creating a vortex. You are done when you have a good head of soapsuds. (The soap will break down the nuclear membrane allowing the nuclear DNA to be released.)