PLATES XLIV-XLIX)" Thus once again we meet, in these lower forms, the spiral organisation which is so common a feature in plants. The conclusion is unavoidable that this prevalence of spiral structure reflects some underlying vital principle that is common to the whole of the plant kingdom " (Astbury and Preston, 1940). MANY kinds of bacteria, usually described as rods, are helices or " spirals ", and the appendages of such bacteria, usually called flagella, are a result of motility and not motile organs. Most of the present work on this subject was done on B. typhosus, but observations on B. proteus, B. megatherium, B. cereus, B. subtilis, B. jluorescens and others indicated that this new conception of shape and motility applies widely. For the purposes of this paper " bacteria " means most of the I ' Eubacteriales ". Bacterial flagella : stained preparationsThe invisibility of flagella with ordinary microscopy has led to the invention of numerous staining methods, satisfactory to their authors, but usually a failure in other hands. Often mucous threads attached to bacteria have been stained and regarded as flagella. Instances are the denial by van Niel (1923-24) of Ellis's claim (1902, that certain sarcinE possessed flagella, and the supposed flagellation of B. tulareme, refuted by Hesselbrock and Foshay (1945). Zettnow, inventor of a much used staining method (1899), admitted later (191%) that he could not always differentiate between " mucous threads " and flagella, especially when mucous threads showed a wavy appearance, and added that such structures should only be regarded as flagella when motility had fist been established ! Hinterberger (1921) similarly warned against confusing what he called " Myzele" with true flagella, but his basis for JOUEN. OF PA%E.-VOL. LVIU 325 Z * JOURB. OF PATH.-VOL. LVIIl

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