The endocrines in general medicine / by W. Langdon Brown.

  • Walter Langdon-Brown
Date:
1927
Catalogue details

Licence: In copyright

Credit: The endocrines in general medicine / by W. Langdon Brown. Source: Wellcome Collection.

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    It might appear that an animal so directed would act like an uncontrolled machine and soon meet with disaster. That this may readily happen is sufficiently illustrated by the behaviour of a moth towards a candle. That it does not invariably happen is due to internal controls apparently of a chemical nature. Thus, Loeb has shown us that bees before the nuptial flight become intensely positively heliotropic, but immediately afterwards the Queen Bee loses this heliotropism and becomes stereo¬ tropic, which leads her to begin a subterranean existence where the new nest is founded. The condition of the gonads here profoundly modifies the tropism of the animal. Animals that are indifferent to light can be made positively or negatively heliotropic by certain chemical substances such as acids, alcohol and caffeine. Thus Daphnia become positively heliotropic in the presence of C02. A caterpillar acquires a positive heliotropism until it is well-fed, when it loses it; in this way it finds the few young leaves at the top of a twig towards which it is driven by its heliotropism ; having eaten these, it is free to move down again until again driven up another twig by the same process. These simple examples show how the conduct of an animal without associative mechanisms (and therefore without consciousness as ordinarily understood) is modified by chemical means. As Loeb says, the theory of tropisms is at the same time the theory of instincts, if due con¬ sideration is given to the role of hormones in producing certain tropisms and suppressing others. THE HORMONES IN FCETAL LIFE. From the nature of the case, the actual demonstration of endocrine activity in foetal life is easier in the frog than in the mammal. Thus the secretion of the thyroid was shown by Gudernatsch to be the chief agent in the transformation of the tadpole into the frog. It is inter¬ esting to note that, if extraneous thyroid is given, the animal’s own gland remains much underdeveloped; evidently the stimulus of having to provide secretion is one of the conditions required for full development of the gland. This suggests the need of caution in
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