196 BENNET M. ALLEN 



ture, increase in size and irregularity in form of follicles. He re- 

 ports a deterioration in the quality of the coUoid^ — a change to a 

 more fluid condition showing an alveolar or fibrous character. 



In my own study of the thyroid gland in thymusless tadpoles 

 no abnormal features as to size or quality were demonstrated. 

 The accompanying table requires some explanation. The heads 

 of the thymusless frogs were cut in serial sections 25// in thickness. 

 The colloid was very tough — thoroughly normal in consistency 

 and offered so much resistance to the knife that the glands were 

 often torn where the knife encountered an especially thick col- 

 loid mass. The length of the thyroid gland in these series was 

 estimated by counting the sections instead of by measuring as 

 in controls nos. 21 to 37. In all the sectioned specimens the 

 thyroid glands appeared to be abnormally short, although of 

 normal width and with follicles of normal character. Since 

 among the specimens thus sectioned, nos. 6 to 14, only nos. 12 

 and 14 were control frogs, we have insufficient means of compar- 

 ing the operated and control frogs among the specimens thus 

 treated. A comparison of these sectioned specimens with meas- 

 ured ones, nos. 1 and 3 and nos. 21 to 37, shows that the sec- 

 tioned ones are almost invariably shorter than broad, while the 

 reverse is true of the dissected specimens. It is quite probable 

 that the toughness of the thyroid glands has caused them to be 

 pulled out a trifle with each stroke against the knife. In this 

 manner, cutting each time a thicker slice of the thyroid region 

 than of the material as a w^hole. Tests showed that the micro- 

 tome used is accurately constructed. By comparing the widths 

 of the thyroid gland in the thymusless and control frogs, there 

 seemed to be no consistent difference between them, and the dif- 

 ference in length favors the controls. The apparently greater 

 size of the thyroid glands of the controls is probably due wholly 

 to these differences in technique. If they have any significance 

 at all, it is quite contrary to the findings of Adler. 



