Reactions of daphnia pulex to light and heat / Robert Mearns Yerkes.

  • Yerkes, Robert M. (Robert Mearns), 1876-1956.
Date:
[1903]
Catalogue details

Licence: In copyright

Credit: Reactions of daphnia pulex to light and heat / Robert Mearns Yerkes. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    body is parallel with the rays of light. Because of the shght depth of the water in the box it was impossible for them to move far in a straight hne when thus oriented wdthout reaching the surface of the water or the bottom of the box. As a result of this condition the animals orient themselves with their heads toward the higher intensity region and swim upward at an angle of about 45° with the surface until they reach the surface; they then cease swimming and by reason of gravity sink toward the bottom of the box; in a few seconds they again swim upward. This is repeated, and thus the animal approaches, by a very indirect, zigzag path, the region of greatest illumination. To the highest intensity (about 20 candle-power) which was obtainable with the apparatus from a 100-candle-power lamp, the Daphnia were uniformly positive in their phototaxis. And apparently when they had reached the -|- end of the band of light they were still trying to move on to a higher intensity. There is therefore no evidence from these experiments of an “optimal intensity.” As it seemed possible that a higher intensity might reveal the “optimal,” further tests were made by simply placing a 100-candle-power lamp at one end of the glass experiment-box. Under these conditions the animals moved directly to the + end of the box. When no adiathermal screen was interposed between the lamp and the box the heat was so great as to kill them within a few seconds after they reached the point nearest to the lamp. But notwithstanding the fact that they were thus directed by the light into a region of exceedingly violent thermic stimulation the Daphnia never turned back. When a screen was used the animals after reaching the + end remained there, moving about in a very irregular jerky manner as if under the influence of a strong stimulus. They have been observed to move about in this way for as long as thirty minutes, within a few centimetres of a lamp whose light was almost too bright for the human eye to endure, without giving any signs of a tendency to become negative to the light. To all appearances the organisms are wholly unable to resist the directive influence of hght, even though it lead them into intensities of stimula- tion far greater than those to which they are accustomed, or into the presence of positively harmful stimuli. In a previous paper (Yerkes, :00, p. 419) I have described the phenomenon of Daphnia being directed by light into harmful chemical solutions. From these observations we learn that Daphnia is positively phototactic to light up to an intensity of 100 candle-power, and that there is no evidence of an “optimal intensity” between 0 and 100 candle-power. 2. The Influence of Heat Accompanying Light.—The following experiments were made to determine (1) whether the radiant heat which accompanies the light from a 16- candle-power incandescent lamp has] any influence upon the motor reactions of