Volume 1

Studies in general physiology / by Jacques Loeb.

  • Loeb, Jacques, 1859-1924.
Date:
1905
Catalogue details

Licence: Public Domain Mark

Credit: Studies in general physiology / by Jacques Loeb. Source: Wellcome Collection.

    21/446 (page 1)
    THE HELIOTROPISM OF ANIMALS AND ITS IDENTITY WITH THE HELIOTROPISM OF PLANTS1 I. INTRODUCTION I intend to show in the following pages that animal movements depend upon light in the same way as the move¬ ments of plants. It is a well-known fact that animals, when light falls on them, move toward the source of light, like the moth, or move away from it, like the earthworm. It is also well known that certain plant organs have a tendency to turn toward or from the source of light when illuminated from one side only. While the conditions which govern the behavior of plants toward light have been well analyzed, especially by Sachs, little has been done to investigate the conditions upon which depend the movements of animals toward a source of light. It is the purpose of this paper to fill this gap, and to enumerate the facts which show that in reality the animal motions called forth by light depend upon the same circumstances as the motions which light produces in plants. The effects of light which we intend to study are purely mechanical, inasmuch as they consist in changes in position, as well as in the direction and the sense of the progressive movements of living animals. Consequently we shall regard as essential such circumstances as can help to explain the mechanical effects of the light. These circumstances, as in the case of all stimulations, are of a double origin: first, those belonging to the stimulus—in this case the light; and, i Pamphlet, Wurzburg, 1889. 1