A simple spinner for roll tubes used in estimating bacterial populations.

In estimating bacterial populations by the colony count method increased accuracy is obtained by using large numbers of replicates. The high cost of Petri plates makes this difficult in many laboratories. A simple spinner is described which utilizes cheap, easily obtained screw-capped bottles to substitute for Petri plates. The method has proved satisfactory in estimating numbers of Rhizobia, and has resulted in significant savings in the cost of glassware and media, and in incubator space.