192 



DUCTLESS GLANDS 



.___ liver* 



pancreas 



.,-Spieen. 



..adrenals 



are produced. Some of the mucous membrane of the small in- 

 testine was scraped off, treated with acid, and injected into the 



blood. Immediately, pan- 

 creatic juice flowed. The 



-pineal body flow is tnou S ht to nave 

 pituitary* been effected by the stim- 

 ulation of the digestive 

 glands by secretin which 

 was probably formed from 

 an inactive hormone in the 

 mucous membrane. 



The internal secretions 

 are of great importance in 

 bringing about coordina- 

 tion among the various 

 organs. It is thought by 

 some investigators that 

 every kind of tissue may 

 give rise to individual sub- 

 stances or principles which pass directly into the blood, and affect 

 the general working or metabolism of the body. Not many studies 

 have been published concerning tissue secretion. To date, in- 

 vestigations have been confined largely to the hormones of the 

 ductless glands. 



It is difficult to secure the internal glandular secretions of human 

 beings in a pure state. Therefore, our knowledge concerning 

 them is based primarily on experimentation on lower animals, 

 chemical examination of the glands and their extracts, and of 

 the blood near the glands, observations of the effects resulting 

 from disturbances of the ductless glands, and effect of direct 

 injections of extracted or synthesized internal secretions. 



The thyroid. The thyroid is one of the ductless glands. It is 

 situated in the neck and consists of two divisions or lobes, one on 



Most of the ductless glands of man are indicated in 

 their approximate positions. 



