invested by peritonaeum; but, whatever be its size, structure, or
position, it may be always distinguished from the bladder by being
devoid of the fibrous tunic, and by having but an indirect relation to
the vesical orifice.

[Footnote: On considering these cases of physical impediments to the
passage of urine from the vesical reservoir through the urethral
conduit, it seems to me as if these were sufficient to account for the
formation of stone in the bladder, or any other part of the urinary
apparatus, without the necessity of ascribing it to a constitutional
disease, such as that named the lithic diathesis by the humoral
pathologists.

The urinary apparatus (consisting of the kidneys, ureters, bladder, and
urethra) is known to be the principal emunctory for eliminating and
voiding the detritus formed by the continual decay of the parts
comprising the animal economy. The urine is this detritus in a state of
solution. The components of urine are chemically similar to those of
calculi, and as the components of the one vary according to the
disintegration occurring at the time in the vital alembic, so do those
of the other. While, therefore, a calculus is only as urine precipitated
and solidified, and this fluid only as calculous matter suspended in a
menstruum, it must appear that the lithic diathesis is as natural and
universal as structural disintegration is constant and general in
operation. As every individual, therefore, may be said to void day by
day a dissolved calculus, it must follow that its form of precipitation
within some part of the urinary apparatus alone constitutes the disease,
since in this form it cannot be passed. On viewing the subject in this
light, the question that springs directly is, (while the lithic
diathesis is common to individuals of all ages and both sexes,) why the
lithic sediment should present in the form of concrement in some and not
in others? The principal, if not the sole, cause of this seems to me to
be obstruction to the free egress of the urine along the natural
passage. Aged individuals of the male sex, in whom the prostate is prone
to enlargement, and the urethra to organic stricture, are hence more
subject to the formation of stone in the bladder, than youths, in whom
these causes of obstruction are less frequent, or than females of any
age, in whom the prostate is absent, and the urethra simple, short,
readily dilatable, and seldom or never strictured. When an obstruction