Image extracted from “Pathogenic micro-organisms. A text-book of microbiology for physicians and students of medicine. (Based upon Williams’ Bacteriology)” (1920) by Ward J MacNeal and Herbert U. Williams and entitled “Bacillus coli showing flagella” (retrieved via flickr.com; contributing library: Cornell University Library; digitizing sponsor: MSN); the image was modified by MIC. The cover is published under the Creative Commons Attribution (CC BY) license.