THE EFFECTS OF CASTRATION 147 



Extirpation of the adrenal bodies, another ductless 

 gland, leads to death. Injury to these bodies causes 

 Addison's disease. 



Finally, the reproductive glands themselves produce 

 internal secretions. In the case of the male mammal it 

 has been shown with great probability that it is the 

 supporting tissues of the glands, and not the germ-cells, 

 that produce the secretion. Likewise, in the case of 

 the ovary, it appears that the follicle cells of the corpus 

 luteum give rise to an important internal secretion. 

 If the sac-like glands are removed, the embryo fails to 

 become attached to the wall of the uterus of the mother. 

 If the ovary itself is removed from a young animal, 

 before corpora lutea are formed, the uterus remains in 

 an infantile condition. 



From a zoological point of view the recent experi- 

 ments of Gudernatsch are important. He fed young 

 frog tadpoles with fresh thyroid glands. '' They began 

 very soon to change into frogs, but ceased to grow in 

 size. The tadpoles might begin their metamorphosis 

 in a few days after the first application of the thyroid, 

 and weeks before the control animals did so." 



In contrast to these effects Gudernatsch found that 

 tadpoles fed on thymus grew rapidly and postponed 

 metamorphosis. They might even, in fact, fail to 

 change into frogs and remain permanently in the tad- 

 pole condition. If thyroid, extracts produce dwarfs; 

 thymus extracts make giant tadpoles that never become 

 adults. 



These examples will suffice to show some of the im- 

 portant effects on growth that these internal secretions 

 may bring about. 



