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.

    54/446 page 34
    justified in taking as the effect of light the movements of the animals to the top of the test-tube ; it might, indeed, be a geotropic phenomenon. To decide this the animals were placed in a test-tube which was lined with thick black paper except for a strip 2 mm. wide. The uncowered strip was turned downward, so that light could enter the vessel only from below. Diffuse- daylight was reflected through the slit from below by means of a mirror. The animals collected in the lower, lighted portion of the glass vessel. Their helio- tropism is therefore more powerful than their geotropism, even when only weak diffuse daylight is used. The geotropic experiments succeed only when the animals have been in the light for some time and have not yet come to rest. When the animals are kept in the dark for a long time and the test-tube is not disturbed, they do not creep upward. The orienting effect of the light always exceeds that of gravity. The effects of gravity, like the effects of light, usually appear only during certain periods in the life of the animals; at any rate, they cannot always be demon¬ strated with certainty. The contact-irritability of the caterpillars of Porthesia chrysorrhoea shows itself by the way in which the animals remain in the corners and convex sides of solid bodies. I covered the boxes in which I cultivated my caterpillars with large, square glass plates. These did not close the box tightly, so that the animals could creep out and creep upon the glass plates. Only rarely, however, were they found on the free surface of the plates. The animals moved along the rough edges of the plate until they reached the window side of the dish. I confirmed this observation almost daily for months. When I placed the animals upon the outside of a cubical block, they collected by hundreds in one of the upper corners. Of course, only a few have room in the corner itself, but, as is generally the case with these ani-
    digitised image 1
    digitised image 2
    digitised image 3