PRESIDENT’S ADDRESS. 31 
creas or as the result of its removal by surgical procedure, its internal 
secretion is not available, sugar is no longer properly utilised by the 
cells of the body and tends to accumulate in the blood; from the 
blood the excess passes off by the kidneys, producing diabetes. 
Another instance of an internal secretion furnished by an organ 
which is devoted largely to other functions is the ‘ pro-secretin ’ found 
in the cells lining the duodenum. When the acid gastric 
juice comes into contact with these cells it converts their 
pro-secretin into ‘ secretin.” This is a hormone which is passed into 
the blood and circulates with that fluid. It has a specific effect on the 
externally secreting cells of the pancreas, and causes the rapid out- 
pouring of pancreatic juice into the intestine. This effect is similar 
to that of the hormones of the pituitary body upon the cells of the 
kidney and mammary gland. It was discovered by Bayliss and 
Starling. 
The reproductive glands furnish in many respects the most interest- 
ing example of organs which—besides their ordinary products, the 
germ- and sperm-cells (ova and spermatozoa)—form 
ra 28 hormones which circulate in the blood and effect 
the repro- § changes in cells of distant parts of the body. It is 
ce through these hormones that the secondary sexual 
characters, such as the comb and tail of the cock, the 
mane of the lion, the horns of the stag, the beard and enlarged larynx 
of a man, are produced, as well as the many differences in form and 
structure of the body which are characteristic of the sexes. The 
dependence of these so-called secondary sexual characters upon the 
state of development of the reproductive organs has been recognised 
from time immemorial, but has usually been ascribed to influences pro- 
duced through the nervous system, and it is only in recent years that 
the changes have been shown to be brought about by the agency of 
internal secretions and hormones, passed from the reproductive glands 
into the circulating blood.” 
It has been possible in only one or two instances to prepare and 
isolate the hormones of the internal secretions in a sufficient condition 
of purity to subject them to analysis, but enough is known 
Chemical about them to indicate that they are organic bodies of a not 
nature of : ; 
hormones. Very complex nature, far simpler than proteins and even 
than enzymes. Those which have been studied are all 
dialysable, are readily soluble in water but insoluble in alcohol, and are 
not destroyed by boiling. One at least—that of the medulla of the 
suprarenal capsule—has been prepared synthetically, and when their 
Duodenum. 
26 The evidence is to be found in F. H. A, Marshall, The Physiology of Repro- 
duction, 1911. 
