Abstract
The attempt has been made to devise methods for investigating the activity and learning capacity of sheep following the extirpation of the thyroid glands. Their intelligence was tested by their ability to learn a simple labyrinth and the twin of each pair making the better record was thyroidectomized by Dr. Simpson. Later, when the operated lambs showed clearly the stigmata of cretinism the pairs were again tested in order, if possible, to demonstrate any influence of hypothyroidism on the intelligence of the operated lamb when compared with its normal twin. A labyrinth with a single cul de sac has been constructed in which, by a system of gates, the position of the cul de sac can be reversed. This arrangement makes possible the presentation of a number of problems so that the tests on a pair of lambs can be continued as long as may be necessary to determine the effect of the extirpation of the thyroid glands on the ability of the operated lamb to profit by experience.
The effect of thyroidectomy on the activity of the lambs was also sought for by comparison of each cretin lamb with its normal twin. It was found practicable to measure the activity of the sheep by attaching a pedometer to the fore leg and calibrating the instrument to measure the number of steps which the animal takes instead of the distance it covers. The pedometer is sufficiently delicate as an indicator of the animal's spontaneous activity to demonstrate lethargy if it occurs following throidectomy. An apparatus has been constructed by which the cretin's capacity for muscular exertion can be compared with that of the normal lamb. It is essentially an inclined plane the angle of which can be altered at will.
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