KACIAL TYPES KEITH. 451 
ing years of the present century. Thej^ Avere seeking to explain ^\ by 
it was that the pancreas poured out its digestive juice as soon as the 
contents of the stomach commenced to pass into the first part of the 
duodenum. It was then known that if acid was applied to the lining- 
epithelial membrane of the duodenum the pancreas commenced to 
work ; it was known also that the message which set the pancreas into 
operation was not convej^ed from the duodenum to the pancreas b}' 
nerves, for when they were cut the mechanism was still effective. 
Bayliss and Starling solved the puzzle by making an emulsion from 
the acid-soaked lining epithelium of the duodenum and injecting the 
extract of that emulsion into the circulating blood. The result was 
that the pancreas was immediately thrown into activity. The par- 
ticular substance which was thus set circulating in the blood and 
acted on the pancreas, and on the pancreas alone, and thus served as 
a messenger or hormone they named secretin. They not only cleared 
up the mechanism of pancreatic secretion, but at the same time made 
a discovery of much greater importance. They had discovered a 
new method whereby one part of the human body could communi- 
cate with and control another. Up to that time we had been like 
an outlandish visitor to a strange city, who believed that the visible 
telegraph or telephone wires were the only means of communication 
between its inhabitants. We believed that it was only by nerve fibers 
that intercommunication was established in the animal body. Bay- 
liss and Starling showed that there was a postal system. Missives 
posted in the general circulation were duly delivered at their des- 
tinations. The manner in Avhich they reached the right address is 
of particular importance for us; we must suppose that the missive 
or hormone circulating in the blood and the recipient for which they 
are intended have a special attraction or affinity for each other — 
one due to their physical constitution — and hence they, and only 
they, come together as the blood circulates round the body. Secre- 
tin is a hormone which effects its errand rapidly and immediately, 
whereas the growth or morphogenetic hormones thrown into the 
circulation by the pituitary, pineal, thyroid, suprarenal, and genital 
glands act slowl}^ and remotel3^ But both are alike in this; the 
result depends not only on the nature of the hormone or missive but 
also on the state of the local recipient. The local recipient may be 
specially greedy, as it were, and seize more than a fair share of the 
manna in circulation, or it may have " stick}^ fingers " and seize what 
is not really intended for local consumption. We can see that local 
growth — the development of a particular trait or feature — is de- 
pendent not only on the hormones supplied to that part but also on 
the condition of the receptive mechanism of the part. Hence we 
can understand a local derangement of growth, an acromegaly or 
giantism confined to a finger or to the eyebrow ridges, to the nose, 
