The true pathogenic fungi occur on the surface of the body, usually attacking the epidermic or epithelial structures, but in some cases penetrating more deeply. They mostly cause lesions of the hairs and epidermis, and some of them lead to inflammations in which the true skin and, it may be, the deeper structures are concerned. The resulting conditions of the skin are described in the Section on Diseases of the Skin.

Achorion Schoenleinii is the fungus of the well-known disease, Favus. It consists almost entirely of hyphse, which form a dense network of threads. Conidia spores of an oval shape and highly refractive are also produced (Fig 160). The fungus has been cultivated on nutrient medium, but it grows best on blood serum. At ordinary temperatures it does not grow at all, requiring a temperature of about 84° F. Hence it is probably an obligate parasite.

Favus is very common, in mice and cats, and it is probably communicated from them to man. It is peculiar that this fungus, whose regular seat is probably the mouse, has a characteristic smell suggestive of these animals. •

The fungus extends into the hair sheath surrounding the bulb and penetrates into the shaft. It also penetrates to the deeper layers of the epidermis and even to the true skin.

Trichophyton tonsurans is the fungus of Ringworm, and of the corresponding diseases of the body and beard, namely, tinea circinata and tinea sycosis. It consists of hyphae and conidia spores, but there is no proper fructification. It has been cultivated on nutrient media, and grows best on blood serum at a temperature of 29° C. The cultures have, by inoculation, produced the typical lesions of tinea circinata.

Fig. 160. - The fungus in favus. Short threads are shown, x 350.

The fungus grows in the epidermis and penetrates into the hair shaft (see under Skin Affections). It also irritates the true skin, producing inflammatory lesions.

Microsporon furfur is the fungus of Pityriasis versicolor. It consists of ramified hyphae and spores, which occur in groups forming grape-like bunches. The fungus penetrates very little into the epidermic layers and produces merely a desquamation without inflammation.

Oidium albicans (also called Saccharomyces albicans) is the fungus of Thrush. It is by some regarded as belonging to the sprouting fungi, although it undoubtedly produces long threads or hyphae. It is in the form of branching threads, and of conidia, which lie in groups. It has been cultivated, and is said to have the power of fermenting sugar.

The fungus grows chiefly in the mouth, forming, with the epithelium, a soft whitish membrane. This is the so-called aphthous condition which sometimes occurs in unhealthy children and even in adults. It may extend to the oesophagus, stomach, and intestine, and to the air passages. The accompanying figure (161) shows the appearances in a case in which the (esophagus was affected. It is said to be capable of inoculation on the mucous membrane of the vagina. Zenker and Wagner have described cases in which the fungus had extended to the blood and caused embolism in the brain.

Fig. 161. - Oidium albicans. The fungus formed a yellow layer on the surface of the d'sophagus and penetrated downwards to the mucous membrane, which was much inflamed under it. x 350.

The position of the disease called Mycetoma and Madura foot is not yet completely determined. Carter asserted that a fungus was the cause of the disease, and the name Chronyphe Carteri was given to the fungus. Kanthack recently described and figured a fungus which he asserted to be a form of Actinomyces. Boyce and Surveyor hold that this fungus is only present in the pale or ochroid form of the disease and that a large branching septate fungus is present in the black variety. The more recent observations of Vincent on a case of the pale variety seem to show that the parasite is not actinomyces but a form resembling this which he designates Streptothrix madurae. He has cultivated it on various media and finds that its behaviour differs from that of actinomyces. (See also page 324).

The disease is characterized by the presence of canals and cavities which penetrate both the soft parts and the bones. These open externally and discharge a fluid which contains black granules in the black form, and yellow granules resembling fish-roe in the pale form. On dividing the foot the passages are visible; in the black form they contain dark-coloured debris and in the pale form granules like those discharged. There is great thickening of the parts and an appearance resembling tubercular disease. The condition is a chronic one, for which amputation is frequently performed.

A disease of the skin closely resembling Lupus, and called Pseudo-lupus, has been described recently as due to a Blastomyces (Gilchrist and Stokes).

Literature

De Bary, Fungi, mycetozoa and bacteria, 1887. Aspergillus, etc. - Grohe, Berl. klin. Wochenschr., 1870; Gkawitz, Virch. Arch., lxxxi.; Lichtheim, Zeitschr. f. klin. Med., vii.; Cassells (Aspergillus in ear, with literature), Glasg. Med. Jour., 1875, vii., 34; Leber, Berl. klin. Wochenschr., 1882; Schubert, Deutsch. Arch. f. klin. Med., xxxvi.; Carter, Mycetoma or the fungus dis. of India (with coloured plates), 1874; Lewis and Cunningham, Fungus dis. of India, 1875; included also in Lewis's Physiol, and pathol. researches, 1888: Moxon and Hogg, Path, trans., 1869, p. 411; Eisenberg, Bakteriolog. Diagnostik, 1888; Kanthack, Journ. of Path., i., 140, 1892; Hewlett, Lancet, 1892, ii.; Boyce and Surveyor, Proceedings of Royal Soc, 1893; Vincent, Ann, de l'lnst. Pasteur, viii., 129, 1894; Gilchrist and Stokes, Jour. Exper. Path., iii., 53, 1898.