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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SUMMARY : During normal movement most motile bacteria carry a straight tail, which, when the movement slows, stiffens into helical structures commonly called flagella. The helices of many kinds of bacteria were photographed with a sunlight darkground microscope, and their wavelengths measured. Mean values and standard deviations were calculated for eacli strain and then for the species. 'Biplicity' (two wavelengths per bacterium, one twice the other) was observed frequently. Each strain appears to have its own constant wavelengths. The wavelength differs in different kinds of bacteria from 0.60 to 5058p., the distribution over the various species not revealing a distinct pattern nor any obvious correlation with other characteristics. The wavelength is affected by temperature, pH value, and colloid content of medium. These features, and the effects of drying, make stained preparations useless for measuring.

This paper describes how microcinematographic pictures were made of the agglutination process of typhoid bacilli (both H and 0), and what the resulting 16 mm. films showed. TECHNIQUEThe technique used was described in detail in a previous paper on the microcinematography. of the motile organs of typhoid bacilli (1940). Here the following chief points may suffice.Sunlight was taken as the source of light. It was brought direct from a heliostat mirror through a 2-meter focus collector lens to the dark ground condenser of the microscope. No further mirrors, nor coolers, nor light filters were employed. This had been proved to be the only way to get sufficient light onto the photographic film.The darkground condenser was the Siedentopf cardioid. Of great help were the combined glass-mica microscope slides, invented by Zeiss, which provide a perfectly clean surface by splitting off a layer of mica. With glass slides it is very difficult to get a perfectly dark background.'The objective used was the Zeiss oil-immersion apochromat, 35 X, N. A. 0.85. In combination with the Zeiss photographic eye-piece 4 X, and a distance of 15 cm. between microscope and cinema film, a magnification of a little over 50 was reached. This proved ample for all details, and low enough to send sufficient light to the photographic film.