effervescence and without leaving the least residue, even when they
are still enclosed in their vesicles. On the other hand, the true
fatty cells suffer in no way when attacked by this acid; they merely
turn a little yellower.

Let us take advantage of this property to operate on a larger scale.
The adipose tissue taken from a number of larvae is treated with
nitric acid. The effervescence is as lively as if the reaction were
taking effect on a bit of chalk. When it has subsided, some yellow
clots are floating on the surface. These are easily separated. They
come from the fatty substance and the cellular membranes. There
remains a clear liquid containing the white granules in solution.

The riddle of these granules was being presented to me for the first
time; my predecessors had provided no physiological or anatomical data
to guide me; great therefore was my joy when, after a little fumbling,
I succeeded in hitting upon their characteristic feature.

The solution is evaporated in a small porcelain capsule, placed on the
hot embers. On the residue I pour a few drops of ammonia, or else
simply water. A glorious crimson colour at once makes its appearance.
The problem is solved: the colouring-matter which has just formed is
murexide; and consequently the powdery substance which filled the
cells was none other than uric acid, or more precisely ammonium urate.

A physiological fact of this importance can hardly stand alone.
Indeed, since this basic experiment I have discovered grains of uric
acid in the adipose tissue of the larvae of all the Hunting Wasps of
our parts, as well as in the Bees at the moment of the nymphosis. I
have observed them in many other insects, either in the larval or in
the perfect state; but in this respect there is none to equal the grub
of the game-hunting Wasp, which is all speckled with white. I think I
see the reason.

Let us consider two larvae which eat live prey: that of the Sphex and
that of the Hydrophilus.[5] Uric acid, the inevitable product of the
vital transformations, or at all events one of its analogues, must be
formed in both. But the Hydrophilus' larva shows no accumulation of it
in its adipose layer, whereas the Sphex' is full of it.

[Footnote 5: The Great Water-beetle.--_Translator's Note_.]

In the latter the duct through which the solid excretions pass is not
yet in working order; the digestive apparatus, tied at the lower end,
is not discharging an atom. The urinary p