698 ANNUAL llEPORT SMITHSONIAN INSTITUTION, 192 8 



fine tubes are the ducts. They join with one another and form larger 

 ducts. These in turn join to form larger ones, until finally the secre- 

 tion finds its way into one or two large tubes which open into one 

 of the body cavities, the mouth or intestine, for instance. The ar- 

 rangement of the ducts is like the stem system of a bunch of grapes — 

 the hollow masses of cells representing the grapes. 



Some, such as the tear glands, the sweat or mammary glands, 

 empty upon the surface of the body. Since the activities of many 

 of these glands are associated with experiences of every-day life — • 

 crying, sweating, salivation, etc. — it is not surprising that they 

 should have been known for so long. They are characterized by 

 two main features. Their secretions are collected by ducts, and 

 through these they are poured either into one of the body cavities or 

 upon the surface of the body. In short, they are glands of external 

 secretion. 



The ductless glands pour their secretions directly into the blood 

 stream. None of their secretions pass outside of the body. They are 

 on this account also called the glands of internal secretion, endocrine 

 glands, or simply the endocrmes. Their secretions are also known 

 as hormones. The cells of these glands take in their raw materials 

 by the front door, the arteries, and after fabricating a most pow- 

 erful chemical material turn the finished product out at the back 

 door, the veins. Thence the hormone is purveyed to all parts of 

 the body. 



These glands are little chemical factories of a marvelous ingenuity ; 

 and what apparently miraculous effects their concoctions can bring 

 about ! Nothing more wonderful was ever dreamed of by the ancient 

 alchemists with their elixirs and potions. It is the action of one of 

 these secretions that paints the plumage of the male bird in such 

 brilliant colors and also prompts its song. Others cause the growth 

 of bone and direct the development of stature along normal lines — 

 overactivity of this or underactivity of that, and a giant or a dwarf 

 is made. Others influence various psychic processes — instinct, emo- 

 tions, and intelligence. In order that mind and body shall be healthy 

 and normal, all the glands must pour their secretions into the blood 

 stream in proper and due proportions; none must be a sluggard, nor 

 yet overzealous in performing its duties. 



Some of the glands are of such a size and prominence that they 

 could not escape the notice of the ancient philosophers. Their uses 

 were pondered and speculated upon, and many fanciful conjectures 

 were made to account for their presence in the body. But their true 

 functions were undreamed of; they were beyond even the imagina- 

 tion of those days. 



Before the discovery of their true functions the control of the 

 various parts of the body was believed to be vested entirely in the 



