METABOLISM 



227 



it directly into the blood, or by both of these, exerts some essential 

 influence over the processes of metabolism. Removal of the organ 

 early in life creates the condition of peculiar idiocy known as cretinism. 

 Extensive disease of this organ in adult years gives rise to a set of 

 similar symptoms called myxedema. The symptoms of this disease 

 may apparently be attributed to the disturbance in the nutritionjof the 

 nervous system and of the connective tissue. Kirshi's work indicated 



FIG. 121 



The circulation of iron. It is possible at least that by some such route as this the iron liber- 

 ated continually from the wearing-out erythrocytes is saved to the organism for re-use. Ingested 

 in the food, it passes into the bone-marrow, is used as part of the hemoglobin in the circulation, 

 is saved by the spleen, made into bile-pigments in the liver, absorbed by the colon, and then 

 made over into hemoglobin. 



that the para-thyroids are embryonal tissue present in the body to 

 serve as substitutes in case the thyroids are diseased. Injection of the 

 extract of the thyroids of animals or even the successful implantation 

 of their living thyroids into the abdominal cavity often cures these condi- 

 tions of cretinism and myxedema. 



The internal secretion of the thymus, which is especially prominent in 

 the fetus and in childhood, appears to have something to do with fitting 



