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.

    56/446 page 36
    6. The effect of temperature on the caterpillars of Por- thesia chrysorrhoca.—The caterpillars of Porthesia chry- sorrhoea behave toward a source of heat in a manner opposite to that in which they behave toward light; they move away from the source of heat. If the animals contained in an opaque vessel are brought in the neighborhood of a hot stove, they leave the side of the vessel which is nearest the stove. Yet the heat does not compel the animals to move in a straight line, as they do when struck by the more refrangible rays of light. This directing effect of the more refrangible rays of the visible spectrum is greater than that of the dark heat rays. In this way it is possible for the same animal which flees from the source of the dark rays of heat nevertheless to move in the direction of the sun’s rays to the sunny side of a vessel. It is a well-known fact that irritability in a tissue is a function of the temperature. I have already mentioned that at a temperature of less than 13° C. the animals are no longer affected by light. It can be shown that heliotropic irrita¬ bility increases with an increase in temperature. If the animals are kept during the day in a room having a tem¬ perature of about 18°, it is found that they no longer respond to light when beyond a certain distance from the window. If, however, the temperature of the test-tube is increased a few degrees, the animals move the more quickly to the win¬ dow side of the tube the higher the temperature. It can easily be demonstrated that the orientation takes place more rapidly, and that the direction of the progressive movements coincides more nearly with the direction of the rays of light, whenever the temperature is raised. If, however, the tem¬ perature is increased to 30° or over, the animals become very restless; they raise the anterior ends of their bodies higher than is usual in their movement, and so decrease the velocity of their progressive movements. The most suitable tern-
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