CREATURES OF MYSTERY 
187 
at the spot where the latter branches into the bronchial tubes; 
and the adrenal glands, at the top of the kidneys. 
These glands all have the characteristics of discharging their 
secretions into the system directly—that is, without passing it 
through a duct or channel. As there is no vessel in the body 
where the secretion could accumulate, the secretion itself is 
invisible. We assume from the structure of the organ only that 
it is a gland. We also see, under the microscope, that the cells 
of the gland tissue secrete something, but we do not see enough 
of what they secrete to determine the color, consistency, and 
other characteristics of the secretion. 
The sweat and sebaceous glands, on the other hand, carry 
their visible and well-known secretions through special excre¬ 
tory channels to the skin. The stomach and salivary glands 
convey theirs in the same way into the alimentary canal. Like¬ 
wise, the liver transmits its secretion, which is stored away 
temporarily in the gall-bladder, by means of the bile duct. But 
if these aforementioned organs are genuine glands, only glands 
without an excretionary duct, what then becomes of their secre¬ 
tions, and where does it finally go? 
Now, these ductless glands, like all other organs, are neces¬ 
sarily connected with the blood circulation. They are sur¬ 
rounded by blood and lymph vessels which support them with 
nourishment and oxygen, and at the same time carry away the 
products that originate in the glands. To differentiate them 
from the glands of external secretion—for example, a sweat 
or salivary gland—their function is named internal secretion, 
or briefly “incretion.” 
The internal secretion necessarily changes the composition 
of the blood as it passes to different parts of the body to take 
care of the distribution of nourishment and oxygen and to 
carry away waste products and carbon dioxide. Naturally, the 
inner secretory products contained in the blood will have an 
influence on all those organs that are nourished by the blood. 
Therefore, the products of the ductless glands are vitally im¬ 
portant to the growth and health of the entire body. Some¬ 
times their influence promotes growth; at other times it re¬ 
tards; but always their influence is to maintain a normal, 
healthy balance. 
