Changing a Right-thread Helix into a Left or Vice-versa;with Demonstration.

Abstract

In an earlier note 1 it was stated that free sections of fibrin filament were observed moving slowly forward and backward over the face of a red corpuscle without turning around; that fibrin filaments exhibited occasionally a faint diagonal striation indicating a left or right screw-thread; that the same filament showed at one time apparently a left thread and at another a right thread or vice versa; and also that a microcyte touching a red corpuscle at the point of attachment of an actively motile fibrin filament or flagellum, moved slowly first in one direction and then in the opposite direction. This reversal of direction in movement can be explained readily by utilizing the observation that a left helicoid apparently changed into a right helicoid, for with a given rotational direction, either right or left, the helicoid moves in one direction in a resistant medium when it possesses a left twist and in the opposite direction when the twist is right-handed.

That a right helix can change into a left or vice versa may be demonstrated easily in a model. If about 6 turns are cut from a small spool of spring-brass wire (B & S 19) a helix, generally right twist, will be secured. If the ends of this helix are firmly held in pin-vises, the coils moderately stretched apart and the helix rotated so that one end rotates slightly faster than the other, then a change of screw-thread will occur if the rotation is such that the coils widen and decrease in number. For example, in a wire helix with a right-hand spiral and rotating to the right (clockwise) under the conditions mentioned above, the change of twist generally shows itself first in one or the other terminal loop.