CHEM'OTAX'IS (Xeo-Lat., from Gk. virtia, Candia, alchemy + taxis, arrangement, from rtiaartv, tassein, to arrange). The sensitive ness of free-swimming organisms to certain chemical substances, by virtue of which they ap proach or recede from the source of the sub stance. Chemotaxis seems to be fundamentally the same as chemotropism (q.v.), though the re aetion is unlike. It has been held that in many organisms the unequal stimulation of different parts of the creature by the diffusing chemical substance causes the motor organs. On one side to act more strongly than those on the other. Thus. the body is swung arcaind in the medium until it is so placed that all sides are equally stimulated. This condition occurs only when the axis of the organism coincides with sonic of the lines of diffusion of the stimulating chem ical compound. Since the motor organs still act, but now equally on all sides, swimming must take place either toward or away from thy source of diffusion. More recent study, however, has shown that with certain substances the or ganisms, swimming in all directions, accidentally pass into the eonstantly increasing sphere of in fluence of the diffusing substance; but as they SW it]] through it, reach the Ihnit, and are about to pass out into the pure solvent again, a re action occurs Nvhiell reverses the movement of the motor organs. The creature, thus seem to re bound from the invisible limit whenever they reach it. The region occupied by the diffusing substance therefore acts as a trap into which they may pass but from which they cannot escape. tither substances repel a given organ
ism. In this ease the reversal of motion occurs as soon as they reach the boundary of the region occupied by the diffusing particles.
Chemotactic sensitiveness is observed, among plants, in zoospores of various alga• and fungi, in sperms of mosses and ferns. and in many bac teria. Fern-sperms are attracted by malic acid and its salts, as well as by ninny salts of the common mineral acids. Sperms of mosses are attracted by cane-sugar. Such reactions may be demonstrated as follows: Very fine capillary glass tubes are prepared, of such diameter that the sperms can swim easily into them. These are cut into lengths of about one centimeter, and one end of each is sealed in the flame. These tubes are submerged in the solution to be tested, and the whole is exhausted of air under an air pump. Air is then allowed to reenter the re ceiver, and the thud is forced into the tubes, leaving only a small bubble of air at the closed end. A drop of water containing the sperms is now mounted on a microscopic slide in the ordi nary way. The tubes just described are placed under the edges of the cover-glass. their open ends inside. After a short time the sperms may be observed swimming toward and into the tubes, or away from them. The mode of response of an organism is profoundly influenced by the con centration of the substance.