_The Purulent Blister._--In the most superficial variety, pus forms
between the rete Malpighii and the stratum corneum of the skin, the
latter being raised as a blister in which fluctuation can be detected
(Fig. 9, a). This is commonly met with in the palm of the hand of
labouring men who have recently resumed work after a spell of idleness.
When the blister forms near the tip of the finger, the pus burrows under
the nail--which corresponds to the stratum corneum--raising it from its
bed.

There is some local heat and discoloration, and considerable pain and
tenderness, but little or no constitutional disturbance. Superficial
lymphangitis may extend a short distance up the forearm. By clipping
away the raised epidermis, and if necessary the nail, the pus is allowed
to escape, and healing speedily takes place.

_Whitlow at the Nail Fold._--This variety, which is met with among those
who handle septic material, occurs in the sulcus between the nail and
the skin, and is due to the introduction of infective matter at the root
of the nail (Fig. 9, b). A small focus of suppuration forms under the
nail, with swelling and redness of the nail fold, causing intense pain
and discomfort, interfering with sleep, and producing a constitutional
reaction out of all proportion to the local lesion.

To allow the pus to escape, it is necessary, under local anæsthesia, to
cut away the nail fold as well as the portion of nail in the infected
area, or, it may be, to remove the nail entirely. If only a small
opening is made in the nail it is apt to be blocked by granulations.

[Illustration: FIG. 9.--Diagram of various forms of Whitlow.
a = Purulent blister.