Volume 1

Studies in general physiology / by Jacques Loeb.

  • Jacques Loeb
Date:
1905
Catalogue details

Licence: Public Domain Mark

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

    38/446 page 18
    There are two methods by which the second fact, that only the more refrangible rays bring about orientation, can be proved, namely, by experimenting with prismatic spectra or with colored screens. All authors who have studied the behavior of plants behind colored screens have obtained the same result—that it is only, or more especially, the more refrangible rays which are heliotropically active. Studies on the behavior of plants in prismatic spectra have led to harmonious results, in so far as they confirm the gross results obtained by using colored screens; yet opinions differ as to the efficacy of the more limited portions of the spectrum. Since for the present I wish to show only that the laws governing the orientation of an animal toward light correspond to the laws governing the orientation of plants toward the same stimulus, it was necessary to use as a basis the really established data of plant physiology, and I therefore shall confine myself to the proof of the fact that the more refrangible rays of the spectrum are exclusively, or almost exclusively, effective. To do this I proceeded as is usual in plant physiology. In order to have only the less refrangible rays act on the animals, I passed the diffuse daylight through a solution of potassium bichromate or ruby glass; to study the influence of the more refrangible rays, I chose cobalt glass or an ammoniacal solu¬ tion of copper. The screens were examined spectroscopically. The dark-red glass which I used completely absorbed the more refrangible rays, and let through only the red, yellow, and a part of the green rays. The dark-blue glass absorbed the less refrangible red and yellow and a part of the green rays, with the exception of a small region in the outer red. Since, however, the heliotropic phenomena appear only weakly or not at all behind dark-red glass, while they occur just as in diffuse daylight behind dark-blue glass, the few red rays which penetrate the dark-blue glass cannot be
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