operations and in nervous conditions, such as
hysteria. The urine is diminished when there is an organic obstruction
in the urinary tract and certain obstructive diseases of the heart,
the lungs and the liver. In these latter cases, there is seen to be a
retention or suppression of urine. In both acute and chronic nephritis
and in certain fevers, the bladder at times must be emptied by means
of a catheter. At other times, the condition is relieved as far as
possible by limiting certain articles of food in the diet. At any
rate, these points must be kept in mind when examining the urine.

~Effect of Food upon the Urine.~--The odor of normal urine is changed
after eating certain foods, such as onions and asparagus. In disease,
the odor of urine has a distinct value as a means of diagnosis;
cystitis gives a foul odor, certain bacteria bringing about a
decomposition in the urine and giving rise to an odor of putrefaction.
In cases where there is a fistula connecting the bladder and rectum,
the urine has a fecal odor.

~Specific Gravity of Normal Urine.~--The density or specific gravity
of urine means the weight of any volume of urine as compared with
that of equal volume of distilled water. The specific gravity of
normal urine varies from 1012 to 1024, that is, in a thousand cubic
centimeters of urine there are found from 11 to 18 grams of solid
material. In health it is necessary to know the amount of urine passed
in twenty-four hours, to be able to judge whether the amount of solids
is too high or too low.

~Specific Gravity of Diabetic Urine.~--In conditions like diabetes
mellitus, where there is a wastage of sugar taking place in the
body--that is, instead of being oxidized to carbon dioxide and water
and glucose, the sugar is passing into the urine without completing
its oxidation--the specific gravity rises in these cases to 1030 and
over, showing distinctly that a greater amount of solid material is in
the urine than is present normally. In chronic Bright's disease and
diabetes insipidus, the specific gravity is low.

~Method of Determining Specific Gravity.~--The specific gravity is
determined by the use of an instrument known as a urinometer. The
urine is poured into a tube and the urinometer is dropped into it. The
different figures are marked upon the stem of the instrument and it is
a simple matter to read off the figures of the level to which the stem
sinks.

~Reaction to Litmus.~--In a former chapter it