300 



CARL RICHARD MOORE. 



VI. GROWTH OF THYROIDS. 



The actual weights of the thyroid glands of each animal of the 

 series are shown in Table II. and the average weight of the glands 

 of each group as well (both thyroids weighed in each case). 



Sexual Differences. -When the average weights of the twelve 

 normal male thyroids (.1518 gram) are compared with the aver- 

 age weights of the nine normal female glands (.1567 gram), we 

 see that the normal female thyroids are approximately 3.2 per cent, 

 heavier than those of the normal males. Since the total body 

 weights of the two groups do not vary more than one gram, it 

 appears that the female guinea-pig thyroids are heavier than the 

 male glands. 



Castration. Comparing the average thyroid weights of the nor- 

 mal males (.1518 gram) with those of the castrated males (.1649 

 grams), the thyroids of the castrated males appear to be 8.6 per 

 cent, heavier than those of the normal animals. But since the 

 body weight of the normal males is 7.6 per cent, greater than that 

 of the castrated males, the relative differences of thyroid weights 

 are really considerably greater than the differences of their actual 

 weights. Hence we may conclude that castration in the guinea 

 pig favors the growth of the thyroids. 



Slaving. The average weight of the normal female thyroid 

 (.1567 gram) compared with the average of the spayed females 

 (.1675 gram) reveals a difference of 6.8 per cent, in favor of the 

 spayed animals. Since the averages of body weight favor the 

 spayed females by only i per cent., we see that elimination of the 

 ovaries favors growth of the thyroids in the females. 



To the writer's knowledge there is no authenticated observation 

 of a sexual difference in the weight of the thyroid gland in any 

 animal. It must be emphasized that results obtained from a com- 

 parison of one or two animals are decidedly unreliable and of 

 little value. 



In all cases where a sufficient number of animals of correspond- 

 ing ages have been compared the variability in weight is such that 

 results of a definite character are not indicated. Thus Livingston 

 C'i6) determined the weights of the thyroid glands in a large 

 number of rabbits, normal and operated, but the degree of weighf 



