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Edgar M. Crookshank Photography of Bacteria (New York: J.H. Vail & co., 1887), Plate IV, Photo I.
Enlargement from a negative taken with Zeiss' DD. From a cover-glass impression-preparation of Proteus Zenkeri. The preparation was stained a very faint violet with methyl violet, and is represented in brown to illustrate the employment of a brown pigment in the autotype process. X 500.