This method was used to extract DNA bands from agarose gels. The bottom of an 1.5 ml microfuge tube is pierced and stuffed with glass wool. The small cut gel pieces are filled into the tube and the tube submerged in liquid nitrogen. This destroys the gel structure. After shock-freezing, the tube is inserted into another one and centrifuged for 15 minutes at room temperature at 13000 rpm to collect the aqueous layer holding the DNA in the lower tube. The DNA solution can now be subjected to a phenol extraction (see section phenol) and ethanol precipitation (see section 2.5.5).