The work of Bayliss and Starling, two English physiologists, was commenced then to test the hypothesis.  They soon found that the experiment could be so devised as to exclude any influence whatever on the part of the nervous tissues, and yet result positively.  Thus, if a loop of intestine was so prepared as to be attached to the rest of the body only by means of its blood vessels, all the nerves being cut, putting some acid into it was still followed by a flow of pancreatic juice, no less marked than when none of the parts about the piece of gut had been disturbed.  It was evident that the stimulus to the pancreas was carried by way of the blood stream.  That the stimulating substance was not the acid itself, was shown by the failure of the reaction to occur when the acid was injected directly into the blood stream.  Since there was this difference in the effects between acid in the intestine and acid in the blood, it was manifest that the active substance must be some material elaborated in the intestinal mucous membrane under the influence of the acid.  So they scraped some of the lining of the bowel, rubbed it up with acid, and injected the filtered mixture into the blood.  They were rewarded by a flow of pancreatic juice greater in amount than any obtained in their other experiments.  From the filtered mixture they isolated in an impure form, a solid substance which, when introduced into the circulation, has a similar action.  To this, of which the exact chemical make-up is as yet an unknown, they gave the name secretin.

Secretin and its properties they used to generalize as a perfectly direct and amply demonstrable example of an internal secretion.  Metaphors are no less valuable in physiology than in poetry.  They declared that the internal secretions appeared to them to be chemical messengers, telegraph boys sent from one organ to another through the public highways, the blood (really more like a moving platform).  So they christened them all hormones, deriving the word from the Greek verb meaning to rouse or set in motion.  As a science is a well-made language, a new word is an event.  It sums up details, economizes brain-work and so is cherished by the intellect.  The study of the internal secretions has advanced by leaps and bounds since it became convenient to speak of them as hormones.  Withal, the brilliant work of Bayliss and Starling stands as the third great foundation stone, the first Claude Bernard’s and the second Brown-Sequard’s, in the architecture of the modern concepts of the internal secretions.

CHAPTER II

THE GLANDS:  THYROID AND PITUITARY

The glands of internal secretion, the history of which, as tools of thought, I reviewed in the previous chapter, have each an interesting evolutionary story.  Without some acquaintance with that story, the rough outline of their physical architecture, and the particular work they are called upon to perform in the body, no adequate understanding of their influence upon types of human nature and personality is possible.