10 
ESSAY ON SECRETION. 
rieath the cells, but separated from them by a thin layer or 
homogeneous matter called the basement membrane. 
In the salivary, pancreatic, and mammary glands, we have 
examples of the termination of the branches of the duct in 
vesicular extremities; in the testes, of the convoluted termina¬ 
tion of the duct; and in the kidneys we find both convoluted 
ducts and vesicular terminations to exist. 
Brunner’s glands in the duodenum, and the buccal, labial, 
and palatal glands, are thought to resemble the pancreatic 
and salivary glands in their structure. 
In the case of the mammary gland, the duct becomes very 
capacious near its free end, and constitutes a reservoir, which 
serves for containing a quantity of the secretion of the gland 
until it may be granted ; and, as in this case, the demand for 
the secretion is not equally constant with the formation of 
the secretion, there are additional arrangements for pre¬ 
venting its escape, but as these are not connected with the 
secretory portion of the gland they do not come within the 
scope of the present essay. 
We have now, however, to consider the structure of two 
glands of a more complex character than those hitherto men¬ 
tioned ; namely, the liver and the kidneys. These will need 
a separate and careful description, but at the same time 1 
shall render each as brief as possible. 
The blood, whence the secretion of the liver is drawn, is 
carried to that gland by a vein—the portal vein. This gland 
thus differs from all others —every gland, with this single ex¬ 
ception, receiving arterial blood from which to form its se¬ 
cretion. 
On reaching the liver, this portal vein gives off numerous 
branches, which, subdividing, ramify through all parts of the 
gland, and in their course through it are enclosed in sheaths 
of areolar tissue which is continuous with a similar tissue on 
the exterior of the gland, and has been called Glisson’s capsule. 
This tissue not only forms sheaths for the branches of the 
portal vein, but also furnishes numerous little septa, which 
divide every part of the gland into small lobules, each lobule 
being described as of the size of a millet seed. From the 
branches of the portal veins which are found traversing the 
gland, plexuses of vessels are given off which are distributed 
upon the outer surface of the lobules and between the lobules, 
constituting the interlobular plexus ; these furnish the se¬ 
creting capillary vessels; and from the capillaries, the blood 
is conveyed by minute veins commencing within the lobule,— 
intra-lobular veins,—into those vessels which convey it to the 
