SUMMARYThe ability of the L-form of two strains of group A streptococci to pass filters was assessed by several methods. From a comparison of the results, and taking into account the plasticity of the L elements, it is concluded that the size of the reproductive elements of the L-form of the group A streptococcal strains investigated probably lies between 0.45 ,u and 0.65 p.

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Slide cultures consisting of small agar blocks were inoculated with the L-forms of two group A streptococci strains GL-8 and AED grown in broth. The size of the L-form elements was measured on photographs taken immediately after inoculation of the slide cultures. The diameter of the elements varied between 0-2 and 3.0,~. The frequency distribution of the diameters has a bimodal form. This bimodality probably represents the size distribution of two classes of L-form elements which can arbitrarily be divided at the diameter of 0.7 p.The reproductive elements of the streptococcal L-forms were found, with a few exceptions, to have a minimal diameter of 0.7 p (average diameter 1-4 and 1.2 p, respectively; standard deviation 0.3 p).Slide culture experiments with concentrated filtrates of 0.45 filters showed that the reproductive elements present in the filtrates ranged in size from 0.8 to I -7 , u with an average diameter of I -2 , u (standard deviation 0.2 p). The filterability of the streptococcal L-form might therefore be mainly due to the plasticity of the L-form elements.

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