The Motion of the Swarm in Proteus Mirabilis

Observations by phase-contrast microscopy upon the swarm of Proteus mirabilis lead to the conclusion that its development is in two stages; at first, as an open mesh of bacterial strands, along which bodies of swarmers migrate in any direction; later, when these meshes have filled up to give a continuous film of bacteria, expansion continues by the growth of the whole body, in the manner of a Medusa-head colony. All parts are in motion, and masses of several hundred units move about within the swarm. The total effect is a general expansion, but the main motion of swarmers at the edges is at right-angles to the direction in which the swarm is extending.