Agricultural Bacteriology Print: Morphology of Bacteria

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Agricultural bacteriology. Bacteriology, Agricultural. 38 MORPHOLOGY OF BACTERIA Spirilla.—The third group is the spirilla (sing, spirillum) and may be likened unto a corkscrew. The spiral may be loosely or tightly coiled or there may be one, two, or many coils. At times the curve may be so slight that the organism viewed under the microscope appears "comma-shaped." More bacilli are known than cocci and more cocci than spirilla. Migula enumerates 833 bacilli, 343 cocci, and 96 spirilla, a total of 1272. Other workers have tabulated more with a similar propor- tional distribution am. Agricultural bacteriology. Bacteriology, Agricultural. 38 MORPHOLOGY OF BACTERIA Spirilla.—The third group is the spirilla (sing, spirillum) and may be likened unto a corkscrew. The spiral may be loosely or tightly coiled or there may be one, two, or many coils. At times the curve may be so slight that the organism viewed under the microscope appears "comma-shaped." More bacilli are known than cocci and more cocci than spirilla. Migula enumerates 833 bacilli, 343 cocci, and 96 spirilla, a total of 1272. Other workers have tabulated more with a similar propor- tional distribution among the various groups. Gradations.—The difference between these fundamental types is at times very slight. In fact the cocci often merge into the bacilli and the bacilli into the spirilla. It is often difficult accurately to distinguish between the various groups, as is exemplified by the fact that at times B. prodigious has been described by one investi- gator as a coccus and at another time by a different worker as a bacillus. This same condition holds for the pneumonia germ and the one causing pear blight, whereas the cholera organism has been described both as a bacillus and a spirillum. Pleiomorphism.—By pleiomorphism is meant a permanent or semipermanent change in the normal form of the organism. The organism may at one time represent a coccus, at another a bacillus, and at still another a spirillum. This led the early writers to believe that there was a mutability of species. The condition is especially likely to occur among some soil organism and much light has been thrown on the subject by Lohnis who finds the life history of bacteria to be only slightly less complex than that of other organisms.. Fia. 7.—Involution forms from bacilli. (From Fliigge.) Involution Forms.—Although the form of bacteria is quite constant under normal conditions, yet there is a tendency with many organ- isms, especially when grown for some time on artificial media, to show abnorma. © Library Book Collection

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