Electric conservative dichroism in bacterial suspensions: experiments on E. coli

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Abstract
Attempts to measure the electric birefringence of aqueous suspensions of E. coli indicated zero effect using the quadratic method of measurement but finite values using the linear detection procedure. This contradiction was shown to be due to a large dichroic effect in the sample. Furthermore, this dichroism is shown to be due to the turbidity losses encountered with such highly scattering particles. For true dichroism, longitudinal measurements should be identical with transverse, perpendicular data. As this was not the case, computations of the turbidity changes for particles which were fully oriented with their long axes along the light path, when the field was applied longitudinally, together with an analysis of the wavelength dependence of the absorbance showed conservative dichroism, that is turbidity changes, to be the true origin of the observed electro-optic changes.