Figure 2: Ethidium bromide–stained agarose gels reveal the absence of size competition ... and add a 3 × 8 mm stir bar. Begin stirring the mixture at 1,000 r.p.m. on the magnetic stirrer.

As the arm spins inside the enclosure, the magnetic fields from the magnet couple with the stir bar inside the mixture, allowing it to spin without any mechanical link to the stirring device and ...