ORGANS OF INTERNAL SECRETION 353 



Mammalia, though it no doubt existed previously in a minor 

 degree. 



As to whether the ovary elaborates more than one specific 

 substance acting as a chemical excitant, nothing is definitely 

 known, but the composition of the corpus luteum (which is 

 dlflerent from that of the rest of the ovary) indicates that the 

 formation of this structure is accompanied by a change in the 

 nature of the ovarian secretion. Lastly, it is possible that 

 the influence of the ovary upon the metabohsm is due partly 

 to this organ being excretory as well as secretory in function, 

 but there is no evidence that this is actually the case. 



The fact that the testis is an organ of internal secretion 

 seems now to be definitely proved. This secretion is probably 

 formed throughout the entire reproductive period of an animal's 

 life ; but, in those animals which experience a periodic rut, it is 

 no doubt at this season that the testicular hormone is produced 

 in greatest abundance. The development of the prostate and 

 the secondary sexual characters, not to mention the growth of 

 the testes themselves, is convincing evidence that this is the case. 



The Effects of Castration upon the General 

 Metabolism 



In view of the facts referred to above it is almost self-evident 

 that castration must exercise some influence upon the general 

 metabohsm of the body since it produces such marked effects 

 upon the primary and secondary sexual characters. Moreover, 

 it is commonly asserted that the removal of the reproductive 

 glands causes a tendency towards obesity both in Man and 

 animals, but it is not quite clear whether this occurs as a direct 

 or an indirect consequence of castration. The deposition of fat 

 which is sometimes seen to take place after the menopause 

 may be regarded as further evidence of a connection between 

 the functional ovaries and the general metabohsm. 



The existence of such a functional correlation is shown more 

 clearly by the effects of ovariotomy upon the bone disease 

 known as osteomalacia.^ The ovaries imdoubtedly exert a 



^ In one case of osteomalacia Kronig removed the ovaries and trans- 

 planted them on to the peritoneum. The result was immediately beneficial ; 



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