We include here those forms of inflammation of the skin which can be traced to the action of microbes, but leaving over those which have the characters of the specific new-formations.

(A) Boil And Carbuncle

A boil is a localized acute suppurative inflammation with a limited necrosis of the cutis. The irritant finds access by the sebaceous glands or hair follicles, and consists of pyogenic microbes. The source of these may be obscure, but in some cases they are derived from contact with the cadaver. The inflammation manifests itself in hyperemia and exudation, so that a localized redness and swelling are the results. A piece of skin in the very centre of the inflamed area dies, and a small abscess having formed, the slough is by degrees discharged along with the pus.

The Carbuncle is similar in its general characters to the boil, but a much larger piece of skin is involved. The slough is therefore of much greater extent. It sometimes happens that the whole piece of skin in its entire thickness dies and is separated as a dry leathery slough. More frequently the necrosis is less extensive in the superficial layers than in the deeper parts, and the slough is discharged through numerous small apertures.

(B) Lesions From Cadaveric Poisons

In the juices of the dead body, when in process of decomposition, there are innumerable bacteria of different kinds. Some of these may attack the skin of the dissector or pathologist, and find a lodgment there. The organisms themselves are of very various degrees of virulence. The fluid in the abdomen after septic peritonitis, such as that which occurs in one form of puerperal fever, for example, teems with micrococci, and this fluid is peculiarly virulent when applied to the skin.

Besides degrees of activity in the virus, there are various degrees in the susceptibility of different persons, and of the same person at different times. A state of exhaustion of the body causes a greater degree of susceptibility, and makes the inroads of the virus when once implanted more vigorous than in persons in ordinary health. The inference from this is, that the best treatment for this condition is to leave off work and at once seek rest and fresh air.

The virus very often finds access to the skin without any breach of surface. When a wound is made during dissection it is usually washed thoroughly and sucked, while bleeding is encouraged; in this way the virus may be washed away. But if it gets into the hair follicles or sweat glands it may lodge and multiply undisturbed.

The results are somewhat various. The most severe is the occurrence of an Acute phlegmonous inflammation, which rapidly goes on to suppuration. In some cases the inflammation spreads upwards, having the characters of an extending erysipelas. In others the characters are more those of angeioleucitis, the virus extending by the lymphatic vessels, by which it may reach the glands. There may thus occur a suppurating bubo of the axillary glands.

An inflammation of the skin resembling erysipelas may spread from the glands so affected, as the virus, cheeked in its upward course towards the trunk by the glands, passes outwards to the lymph spaces around. This course of events is shown in the account which Paget has given of his own case in his "Clinical Lectures and Essays." The inflammation may travel along the connective tissue of the skin and subcutaneous tissue, and may even reach the pleura. In the skin its ■ effects may be very severe, resulting in sloughing and profuse suppuration like that in erysipelas. It may even lead to septic infection or pyaemia.

A less severe and more local result is the formation of Boils at the seats of inoculation. At first there is usually a superficial pustule, but from this the infection is apt to spread downwards into the deeper layers of the cutis and produce the necrosis and suppuration described above as the phenomena in boils. In other cases the inflammation does not result in necrosis and suppuration, but has a more chronic course, producing what is sometimes called a blind boil, namely, an inflammatory thickening with considerable elevation.

The Pathological wart is really a tuberculosis of the skin, see later.

(C) Phlegmonous Inflammations. Erysipelas

These names are given to acute infective inflammations of the skin. In the case of erysipelas the virus depends on the streptococcus erysipelatis which multiplies more or less abundantly in the lymph spaces and vessels of the skin (see Fig. 479) and subcutaneous tissue. The result is a more or less severe inflammation. At first there is an inflammatory hyperemia, which advances as the virus propagates along the lymph spaces. This, with a moderate exudation of fluid and leucocytes, may be all. But sometimes there is a much more intense inflammation. The skin is infiltrated with leucocytes to such an extent that it is softened and opened out with pus. The epidermis is raised by exudation so that vesicles or pustules are formed. Sometimes the lymph spaces are occupied with fibrine. Besides suppuration, there is often necrosis of portions of the skin so that sloughs are separated with the pus.

A somewhat similar phlegmonous inflammation sometimes occurs around septic wounds, just as we have described in cadaveric infection.

(D) Soft Chancre, Ulcus Molle

This, which is the ordinary non-syphilitic venereal chancre, is usually situated on the organs of generation. It is an acute infectious inflammation, which tends to spontaneous recovery. In about 24 hours after infection a vesicle or pustule appears, which rapidly, by loss of the epithelium and molecular necrosis of the cutis, is transformed into an ulcer of small size. It increases in size and sometimes by infection leads to others. The ulcer sometimes shows much excavation, so that the skin is partly undermined. There is frequently an extension to the neighbouring lymphatic glands, the result being a suppurating bubo.

Fig. 479. - From the skin in a case of erysipelas. The upper illustration shows a lymphatic vessel at the border of a sebaceous gland, filled with micrococci. The lower shows a straight vessel similarly filled, x 350.

The soft chancre usually heals in about 2 to 4 weeks, and does not give rise to syphilis. On the other hand there may be a simultaneous infection with syphilis, and the hard chancre, which is of slow development, may supervene in 3 or 4 weeks.

Ducrey and Unna have asserted that the infection of the soft chancre is related to a specific microbe which has the form of a bacillus growing in chains (Streptobacillus).

(E) Malignant Oedema

This depends on the action of a specific microbe, the bacillus of malignant oedema already described. The affection usually attacks open wounds, and the most typical result is an advancing gangrene with development of gas, accompanied by acute inflammation.

(F) Splenic Fever Or Anthrax

This disease also depends on a special bacillus, which, however, usually extends to the blood, and the patient dies from the general specific fever. There is usually a local affection to begin with, and the disease may remain local. The local affection has the characters of a phlegmonous inflammation of the skin and subcutaneous tissue. Sometimes the appearances of malignant oedema are produced. From these local manifestations the condition is sometimes called Malignant pustule.

(G) Hospital Gangrene

This is an infective disease accompanied by sloughing of the skin. It is due to a specific virus which is supposed to be a micrococcus. The disease occurs in unhealthy hospitals especially in time of war. It attacks open wounds, especially granulating wounds, and is accompanied either by sloughing or molecular necrosis. The gangrene frequently travels along the loose connective tissue and so may undermine the skin, or isolate muscles and blood-vessels.