The cavities are filled with a mass of fungus, red internally, but having an external coating of black. In its mature form the fungus consists of minute articulated threads, branched, and filled with grumous matter.

The spores contain an oil globule at either extremity, and germinate very rapidly.

Trichophyton tonsurans is formed of filaments arranged in rows. The spores originate within the filaments, and are seen as minute round bodies placed at short intervals.

The fungus penetrates the roots of the hair, spreading in an upward direction, causing small elevations upon the scalp. The hair ultimately breaks off at the epidermis.

The disease is termed Herpes tonsurans.

To obtain the fungus, it is necessary to pull out some of the diseased hairs, as it never occurs among the epidermoid scales of the scalp.

The annexed drawing represents a hair filled with the spores of Trichophyton tonsurans.

Fig. 214.

Microsporon andonini surrounds the hair outside the follicle, instead of being developed at the root. Masses of it are sometimes heaped up around the openings of the follicles.

The fungus consists of numerous curved branches and filaments, to which small spores without any granules in their interior are found adhering.

The situation of the parasite suffices, however, to distinguish it from Trichophyton tonsurans.

Allopecia, or loss of hair, is the result of the growth of Microsporon andonini. The hairs become brittle and break off.

Microsporon mentagrophytes has larger filaments and branches, as well as larger spores, than the preceding.

root.

The fungus attacks the hair of the beard, penetrating to the The hair becomes covered with yellowish and grey scales, its connection with the sheath is destroyed, it is rendered loose, and sometimes falls off spontaneously.

A drawing is given of this fungus below.

Fig. 215.

Microsporon mentagrophytes.

S

Microsporon furfur is associated with Ptyriasis versicolor, indicated by the formation of yellowish spots upon the skin of the chest and extremities. The spots increase from the size of a pea to the breadth of six or seven inches.

Under the microscope the fungus will be discovered in the upper horny layer of the epidermis of the affected parts. Acetic acid or caustic ammonia may be employed in the microscopic investigation.

The parasite is composed of long branched filamentous cells. The spores are often collected in groups, as shown in the illustration; they are highly refractive, and appear to be surrounded by two concentric lines.

Achorion Schönleinii is found in favus, attaching itself to the bottom of the hair follicle, the spores being distributed over the root of the hair and upon the surface of the epidermis, round the favus crust. The bulb of the hair is often pointed, and frequently splits up into fibres.

Fig. 217.

Achorion Schönleinii.

The mycelium of the fungus is formed of small tubes with partitions branched in all directions.

The spores are round or oval, and sometimes grouped together, as shown in the illustration. (Fig. 217.)

ALGE.

Cryptococcus cerevisiæ, Torula cerevisiæ, Yeast-plant. This plant is found in fermenting fluids, in yeast, and in saccharine urine. It occurs also in the mouth, œsophagus, and stomach.

It consists of numerous round or oval cells, containing in their interior minute granules resembling excessively minute oil globules.

The mode of propagation is by a species of budding; each cell gives forth one or two minute projections, which become perfect cells, and again develop other buds. In a few hours a row of five or six cells will be developed from a single one.

Fig. 218.

Torula cerevisiæ.

When found in any of the fluids, it indicates the existence of saccharine fermentation.

Sarcina ventriculi is composed of small square bodies, like wool-sacks, heaped together to form square masses, which consist of four, eight, sixteen, or sixty-four cubic cells (gonidia).

Each cell is marked by cross lines or depressions, which

apparently divide it into four portions. Sometimes the cells are round, oval, or even triangular, but always with the corners rounded off.

The illustration represents several forms of the plant.

Fig. 219.

Various forms of Sarcina ventriculi.

Sarcina has been found in the human subject in the vomit, fæces, urine, pus of an abscess, and in the anterior chamber of the eye.

It may give rise to few or no symptoms; it may occur but once in the vomited matters, or, on the other hand, it may continue for weeks, and ultimately cause death from the constant vomiting it sometimes induces.

In order to discover it, the vomited matters should be allowed to rest for a time, and then both the serum on the surface and the sediment at the bottom of the liquid examined on a glass slide under a high power, as the little sac-like bodies are very minute, and may escape detection.

The fluid in which sarcina is found is usually fermenting, and sometimes it is of the consistence of pea-soup and has a brown or green appearance.

This species of alga is easily prepared by being put up in a drop of Canada balsam.

Leptothrix buccalis is found upon the tongue and in the masses of food which are sometimes allowed to collect between the teeth. The parasite is composed of fine filaments, sometimes attached to a stem. Under a very high power small granules may be seen in it.

From the healthy mouth the leptothrix may be obtained by