EFFECT OF EXTIRPATION OF THYROID 591 



each drawing a scale was placed under the microscope and the 

 scale of magnification for that particular drawing indicated on 

 the card with the drawing. This furnished a check on the 

 adjustment of the camera lucida. 



The pituitary gland was taken from the same specimens as 

 was the thymus. Some of the specimens were injured in manip- 

 ulation and in those cases the measurements of the destroyed 

 glands can not be given. The procedure in the measuring of 

 the pituitary gland was the same as for the thymus until it was 

 advisable to measure the dissected gland. In these stages 

 the pituitary is much smaller than the thymus and harder to 

 handle. The most satisfactory method was to dissect the 

 whole brain and take it out of the specimen with the pituitary 

 gland attached. The dura mater was carefully removed to 

 expose the gland as much as possible. The gland was first 

 drawn from its ventral aspect and then from the lateral aspect 

 by the same instruments as were used in measuring the thymus. 



The same methods were applied to the thyroidless specimens 

 which had been prepared by Dr. Allen in the spring of 1916. 

 These specimens were killed as needed over a period extending 

 from a few da3^s after removal in April 1916 to March 1917. 

 The oldest operated tadpole was killed early in March. None 

 of the thyroidless tadpoles metamorphosed into frogs and the 

 comparisons in the later stages are between thyroidless tadpoles 

 and normal frogs of about the same age as the experimental 

 animals. 



In determining the difference in size of the glands in the thy- 

 roidless and the control animals it is necessary to use a standard 

 of comparison rather than the actual volumes because of the 

 method adopted. The three dimensions obtained by the 

 method outlined in the preceding paragraphs were multiplied 

 together which gives the volume of a parallelopiped of those 

 dimensions. Since conditions were uniform in the measuring 

 the same relative error would apply to all. When the glands 

 vary much from the average of the class to which they belong 

 due to irregular contour the difficulty can be adjusted by ref- 

 erence to the drawings. Correction for body length was made 

 by dividing the volume by the body length. 



