_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. b = Suppuration at nail fold. c = Subcutaneous whitlow. d = Whitlow in sheath of flexor tendon (e). ] _Subcutaneous Whitlow._--In this variety the infection manifests itself as a cellulitis of the pulp of the finger (Fig. 9, c), which sometimes spreads towards the palm of the hand. The finger becomes red, swollen, and tense; there is severe throbbing pain, which is usually worst at night and prevents sleep, and the part is extremely tender on pressure. When the palm is invaded there may be marked œdema of the back of the hand, the dense integument of the palm preventing the swelling from appearing on the front. The pus may be under such tension that fluctuation cannot be detected. The patient is usually able to flex the finger to a certain extent without increasing the pain--a point which indicates that the tendon sheaths have not been invaded. The suppurative process may, however, spread to the tendon sheaths, or even to the bone. Sometimes the excessive tension and virulent toxins induce actual gangrene of the distal part, or even of the whole finger. There is considerable constitutional disturbance, the temperature often reaching 101° or 102° F.