No. 508] MECHANISM FOR ORGANIC CORRELATION 215 



ate with the changes in the state of this gland. Our nor- 

 mal skin and features are thus dependent upon the in- 

 tegrity of this internal organ. 



The mechanism of correlation between two such organs 

 as the thyroid and the skin has already been somewhat 

 worked out. It is natural to suspect that this correla- 

 tion is nervous, for both thyroid and skin are supplied 

 with an abundance of nerves coming from a common 

 central organ. But the fact that the symptoms already 

 described as the result of the removal of the thyroid can 

 be checked and even made to disappear by grafting into 

 the animal that has lost its thyroid, a part of a living 

 gland from another animal, shows conclusively that the 

 nervous system is not concerned. The further observa- 

 tion that animals devoid of thyroids may be kept in 

 normal condition by injecting thyroid juice into them 

 or even by feeding them with fresh thyroid glands from 

 other animals, has suggested the idea that this gland 

 produces a substance which makes its way into the blood 

 and is thus carried to those parts of the body where it 

 is needed. It is through this substance that the skin is 

 influenced in that in the absence of this material the skin 

 suffers serious change. The mechanism of correlation 

 between the thvroid gland and the skin, then, consists m 

 a substance produced by the gland and carried m the 

 fluids of the body to various organs, including the skm, 

 whose growth and appearance is thereby modified. 



Similar observations have led to a like conclusion con- 

 cerning the action of the suprarenal bodies and the 

 hypophysis. These organs, like the thyroid produce 

 substances that make their way into the fluids of the 

 body and influence its structure and action in so profound 

 a way that they are absolutely essential to its continued 

 existence. In the case of the suprarenal bodies the active 

 substance has been isolated and is lmown as adrena hn. 

 Since these internal secretions have the power of calling 

 forth or exciting very marked changes m the body tba> 

 have been given the general name of hormones. It would, 



