Normal and Thyroidectomized Sheep. 343 



These experiments demonstrate the existence of a definite 

 stimulus attracting developing nerve fibers within the spinal cord. 



The explanatory theories of Cajal, Kappers and his students 

 and Child seem inadequate. It is hoped that further work on this 

 problem, now under way, will give a decisive answer to this ques- 

 tion. 



164 (191 1) 



Methods of estimating the activity and intelligence of normal and 

 thyroidectomized sheep. 



By H. S. LID DELL (by invitation). 



[From the Physiological Laboratory, Cornell University Medical Col- 

 lege, Ithaca, N. Y.] 



The attempt has been made to devise methods for investiga- 

 ting 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. Simp- 

 son. Later, when the operated lambs showed clearly the stig- 

 mata 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 nor- 

 mal 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 suffi- 

 ciently delicate as an indicator of the animal's spontaneous ac- 



