Forced movements, tropisms, and animal conduct / by Jacques Loeb.

  • Loeb, Jacques, 1859-1924.
Date:
[1918], ©1918
Catalogue details

Licence: Public Domain Mark

Credit: Forced movements, tropisms, and animal conduct / by Jacques Loeb. Source: Wellcome Collection.

    18/222 (page 14)
    locomotor apparatus permit. If, however, the velocity of chemical reactions in one side of the body, e.gin one eye of an insect, is increased, the physiological symmetry of both sides of the brain and as a consequence the equality of tension of the symmetrical muscles no longer exist. The muscles connected with the more strongly illuminated eye are thrown into a stronger tension,a and if now impulses for locomotion originate in the central nervous system, they will no longer produce an equal response in the symmetrical muscles, but a stronger one in the muscles turning the head and body of the animal to the source of light. The animal will thus be compelled to change the direction of its motion and to turn to the source of light. As soon as the plane of symmetry goes through the source of light, both eyes receive again equal illumination, the tension (or tonus) of symmetrical muscles becomes equal again, and the impulses for locomotion will now produce equal activity in the symmetrical muscles. As a conse- quence, the animal will move in a straight line to the source of light until some other asymmetrical disturbance once more changes the direction of motion. What has been stated for light, holds true also if light is replaced bv any other form of energy. Motions caused by light or other agencies appear to the layman as expres- sions of will and purpose on the part of the animal, whereas in reality the animal is forced to go where carried by its legs. For the conduct of animals consists of forced movements. The term forced movements is borrowed from brain physiology, where it designates the fact that certain ani- mals are no longer able to move in a straight line when a We are speaking of positively heliotropic animals exposed to only one source of light.