(1)It was experimentally shown that the pattern of angular distribution of light scattered by moderately large microbial cells is roughly presented by the FRAUNHOFER diffraction theory for a circular slit.
(2) When a parallel beam is used as the incident rays, cuvettes of usual size give, however, smoothed scattering pattern due to the finite effective volume of scattering centre. The light was shown still to be strongly scattered as theoretically expected into the forward direction.
(3) Practically all the scattered light could therefore, be collected by using a light receiver with a large aperture placed close to a thin cuvette. providing thus a convenient method of obtaining the true absorption spectra of cell suspensions.
(4) In accordance with RAYLEIGH-GANS' first approximation to the cross section of microbial cells of moderate size, the total extinction is given by the sum of scattering and absorption attenuation. A true scattering spectra, therefore, could be obtained as the difference of the extinction spectra observed with a usual narrow beam spectrophotometer and the true absorption spectra obtained by use of a wide angle apparatus such as the one mentioned above.
(5) Even in the case of fairly high-populated suspension of
Chlorella, the observed apparent absorption spectra are mostly due to scattering loss. The local feature of the curves reflects the mode of anomalous dispersion of the real part of refractive indices of cells.
(6) A slow rise experienced in the spectrum of yeast at 450mμ is also mainly due to scattering interference and partly to the existence of anomalous dispersion of refractive indices. In the single scattering region, the absorption of cell contributes to the attenuation only through modifying the real part of refractive index and not directly through its imaginary part.
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