The action of light on culture media.

Failure of growth of staphylococci on nutrient agar plates was shown to be due to previous exposure to sunlight in an exceptionally well lit laboratory. Such plates inhibited the growth of Staph. aureus, Staph. albus, some Proteus species and Providence, but not that of various other bacteria. The affected species are found to be more susceptible to the action of hydrogen eroxide added to the medium. The effect was produced in plates of five different nutrient agars, but not in two others which contained casein. Plates awaiting inoculation should be protected from light; a white fabric blind was found not to be fully protective.