November 24, 1916] 



SCIENCE 



757 



at least a week after the operation, long after 

 complete recovery, and it was not evident in 

 certain cultures so long as they were kept in 

 well water, appearing only after they were 

 placed in our city water. 



The interesting thing is that other tadpoles 

 that had undergone a more severe operation in 

 the removal of the thyroid gland showed no 

 appreciable mortality until after the lapse of 

 a month, when they had grown so large as to 

 crowd the aquaria. These were kept in con- 

 ditions identical with those under which the 

 tadpoles deprived of the hypophysis showed 

 such heavy mortality. 



I propose next spring to determine if pos- 

 sible whether this lack of resistance is of a 

 general character or whether the absence of 

 the hypophysis causes a heightened suscepti- 

 bility to specific injurious substances or con- 

 ditions. 



These experiments upon removal of the hy- 

 pophysis represent only one phase of my work; 

 similar methods were applied to the extir- 

 pation of the thyroid anlage. This was re- 

 moved at a slightly later stage 6-6.5 mm. total 

 length shortly after it appeared. In this case 

 a transverse cut was made between the heart 

 and the thyroid anlage and the latter was read- 

 ily removed. In some instances a small por- 

 tion of it may have been left behind, but in 

 the main the operation proved successful as 

 demonstrated in sections of operated tadpoles. 

 Recovery from the operation was quite as 

 rapid and complete as in the case of hy- 

 pophysis extirpation. This operation was suc- 

 cessfully performed upon 336 tadpoles. 



As indicated above, for a long time after the 

 operation the tadpoles showed no ill effects 

 from the absence of the thyroid gland as re- 

 gards either size or vitality. In fact they ap- 

 peared in every way normal up to the time 

 when the hind limbs began to form. When 

 they began to die as a result of overcrowding 

 and other unfavorable conditions that became 

 marked at about 6 weeks after the operation, 

 there was an even greater mortality among the 

 controls. 



The metamorphosis of the controls began 

 about the middle of July and continued to 

 August 13, when the last control tadpole meta- 



morphosed. Five of the operated tadpoles 

 metamorphosed at about the same time as the 

 controls. One metamorphosed much later — 

 September 20. 



At the present date, October 1, twelve oper- 

 ated tadpoles ranging in length from 85 mm. 

 to 123 mm. are living and show no tendencies 

 toward metamorphosis. The hind-limb rudi- 

 ments are rather uniformly about 4 mm. in 

 length. The knee is evident and the toe points 

 distinguishable. The larval characters as a 

 whole are maintained. The intestine, the 

 mouth, eyes, etc., are all larval in character, 

 although a peculiar modification in the form of 

 the head is noted in that the portion in front 

 of the eyes is lengthened, broadened and flat- 

 tened dorsoventrally. It is thus clear that the 

 removal of the thyroid gland has caused these 

 tadpoles to remain in a larval condition for a 

 month and a half after the controls have com- 

 pleted metamorphosis. Section of 7 operated 

 tadpoles at various stages from 9 to 24 mm. 

 showed no vestiges of the thyroid gland. A 

 careful study of the operated animals that have 

 undergone metamorphosis is being carried on 

 to determine whether small portions of the 

 gland have remained after the operation or 

 whether there may not have been new forma- 

 tion of thyroid tissue. Upon sectioning one 

 of these a single well-developed thyroid gland 

 was found on one side. This clearly shows 

 that we were here dealing with a case of im- 

 perfect removal. 



The results of this experiment establish a 

 corollary to the experiments by which Guder- 

 natsch and others have shown that thyroid 

 feeding — hyperthyroidism — greatly accelerates 

 metamorphosis. Conversely, in the absence of 

 the thyroid gland metamorphosis is at least 

 greatly retarded. How long this may continue 

 remains to be seen. 



A careful study of the material is being 

 made to observe the effects of the removal of 

 these glands of internal secretion upon the 

 body as a whole and upon the various organs. 

 The results should be especially interesting 

 becatise we are dealing with material in which 

 the earliest anlagen of these glands have been 

 removed. Bennet M. Allen 



University op Kansas 



