PHYSIOLOGICAL PROPERTIES OF THE GONADS. 30! 



variability was so pronounced that no definite conclusions were 

 warranted. Hatai ('18) definitely states that there is no apparent 

 sexual difference in the weight of the thyroids in the rat. Fur- 

 thermore, the variability in thyroid weight was so pronounced 

 among the operated rats that results of a definite character were 

 not indicated. 



In the guinea pig comparison of the average weights of male 

 and female thyroids at the end of one year favored the females to 

 a slight extent. 



Gonadectomy apparently favors the growth of the thyroid in 

 the guinea pig inasmuch as each operated group showed a definite 

 increase in the thyroids at the end of one year. However, in view 

 of the many failures to establish a definite effect, one must be very 

 skeptical indeed in applying these results as a general effect of 

 gonadectomy. Obviously repetition of the experiment is neces- 

 sary before general principles can be held as established even for 

 the guinea pig. 



VII. GROWTH OF ADRENALS. 



The individual weights of the adrenals (two in each case) can 

 be seen by reference to the different groups given in Table II. 



Sc.rual Differences. When one compares the average weight of 

 the normal male adrenals (.8286 gram) with the average weight 

 of the normal female adrenals (.6894 gram), it is apparent that 

 there is a considerable difference in the two sexes ; the normal 

 male adrenal weights are approximately 20 per cent, greater than 

 those of the normal females, the average of the body weights of 

 the two sexes being almost identical. 



Castration. The average normal male adrenals (.8286 gram) 

 compared with the average castrated male adrenal (.7538 gram) 

 is 9.9 per cent, heavier. However, when average body weights 

 are compared, one sees that the normal male is 7.6 per cent, 

 heavier ; the relative difference, therefore, is seen to be very small, 

 though favoring slightly the normal animals. It appears, there- 

 fore, that castration inhibits the growth of the adrenals to a slight 

 extent. 



Spaying. When the average weights of the normal female 

 adrenals (.6894 gram) are compared with the average weights of 



