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.

    55/446 page 35
    mals, when a few have collected in a spot the others on arriving hold fast to the sides of those already there. An animal at rest acts upon a creeping one as a convex edge. On the other hand, I have never observed that the animals within the cubical box collect on concave edges. From this it follows that the friction of gliding over the convex corners is the source of the stimulation which compels the animal to come to rest there ; in moving over the concave corners this friction, of course, does not take place. These three forms of irritability control mainly the daily life of the animals. We find them in great numbers in fruit trees and bushes, where they pass the winter in their nests: as soon as the warm weather comes, thev leave their nests. Positive heliotropism and negative geotropism com¬ pel them to creep upward to the tips of branches, and contact- irritability holds them fast on the small buds. We can easily show that neither smell nor a special mystical “instinct” leads the animals to the buds, as we are able to compel them by the aid of light to starve in close proximity to food. The animals move to the window side or to the top of a test-tube in which they are kept. If then a branch covered with buds is pushed into the test-tube on the room side, the animals nevertheless remain where light and gravi¬ tation have compelled them to go and are holding them. If, however, they once are on the buds, the latter act as a stimulus which may be even stronger than the light. It is in such a case impossible to draw the animals away from the food by means of light. All these forms of irritability can best be demonstrated on animals which have just left the nest in which they have spent the winter, and which have not yet eaten anything. As soon as they have eaten and are about to moult, their irritability decreases, and at the time of moulting it is almost impossible to show any effect of light or gravity upon them.
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