Multichannel photometer-nephelometer.

We describe an instrument for monitoring either transmitted or scattered light intensity, or both, simultaneously on up to eight channels. The use of a laser light source (at 632.8-nm wavelength) provides high accuracy and dynamic range: optical density can be measured from 0.0004 up to 6, and a scattered light fraction down to 10(-6) can be resolved. Built-in thermostat and magnetic stirrers allow precise monitoring of aqueous microbial growth over a practical range of 4 orders of magnitude of cell concentration.