The finger used to control the delivery of liquid from a pipet is the

The pipettes can basically be characterized into five grades. these grades includes the serological, disposable, repeat, single channel and multi-channel pipette. The guidelines for the usage of each of these pipettes differ. However, some instructions are common, such as the control of the flow of liquid. The index finger is used for the purpose of controlling the flow of the liquid from the pipette.

Hence, the answer is 'index finger'.