Forced movements, tropisms, and animal conduct / by Jacques Loeb.

  • Jacques Loeb
Date:
[1918]
Catalogue details

Licence: Public Domain Mark

Credit: Forced movements, tropisms, and animal conduct / by Jacques Loeb. Source: Wellcome Collection.

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    ture of their body was, therefore, designated as the tropism theory of animal conduct. We started with symmetrical animals since in their case the analysis of conduct is comparatively simple; the results obtained in the study of these symmetrical organisms allow us also to understand the conduct of asymmetrical animals. We shall see that the principles underlying their conduct are the same as in the case of symmetrical animals, the asymmetry of the body altering only the geometrical character of the path in which the animal is compelled to move, not, however, the mechanism of conduct. While a perfectly symmetrical organism, possessed of positive lieliotropism, moves in a straight line to the source of light, the path deviates from the straight line in the case of an asymmetrical organism and may in some cases, as, e.g., in Euglena, be a spiral around the straight line as an axis. Some authors have tried to use asymmetrical organisms as a starting point for the analysis of conduct, but since it is impossible to understand the conduct of the asymmetrical organisms unless it is based upon that of the symmetrical animals, these authors have been led to anthropomorphic specula- tions, such as “ selection of random movements ” which, as far as the writer can see, cannot even be expressed in the language of the physicist. Although the tropism theory of animal conduct was offered thirty years ago 285> 286> 287 its acceptance was delayed by various circumstances. In the first place, the majority of the older generation of biologists did not realize that not only the methods of the physicist are needed but also the physicist’s general viewpoint con- cerning the nature of scientific explanation. In many cases the problem of animal conduct is treated in a way
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