PART IV.

L. MYCOSES (INFECTIONS WITH FILAMENTOUS AND BUDDING FUNGI).

An incomparably lesser rôle in the etiology of disease is played by the filamentous fungi (molds) and the budding fungi than by bacteria (fission-fungi). The diseases generated by the former are designated mycoses.

MORPHOLOGY AND BIOLOGY OF THE FILAMENTOUS AND THE BUDDING FUNGI.

The filamentous fungi are chlorophyl-free, thread-like cells that exhibit progressive apical growth, and that, singly or branched, usually divided into segments by internal septa, unite to form a deposit and at times a dense feltwork of closely interlaced threads (hyphe). This so-called vegetative portion of the fungus is known as thallus (fungous deposit) or mycelium. Distinct from this is the fructifying portion, the fruit-bearer, which arises from the mycelium and bears the fruit (spores or conidia). The spores again grow into threads; the enlargement takes place steadily through progressive apical growth of the threads, which in turn give rise to new spores. The structure of the fruitbearing apparatus is so peculiar in a number of filamentous fungi that this external feature has been made the basis of their classification. Of the numerous species of filamentous fungi, running up into thousands, only the following are of pathologic interest :

1. The Aspergilli (Bulbous Molds).—The fruit-hyphæ exhibit no division; they swell into the form of a club at the extremity. This bulbous enlargement is densely occupied by short, flask-shaped structures, arranged radially, the in

termediate fruit-bearers (sterigmata), upon which the consecutive spores are seated.

2. The Penicillii (Brush-molds).-The fruit-bearers, which generally arise vertically from the mycelium, are transformed, through manifold forked divisions in their upper third, into dense tufts of brush-shaped, ramifying, delicate processes (basidia), upon whose extremities the conidia are seated in long rows in the form of globules.

3. The Mucorini (Globular Molds).-The fruit-bearers, which are mostly unsegmented and undivided, arise vertically from the mycelium and present at their extremity a large spore-mother-cell (sporangium), which is separated from the fruit-hypha by a septum markedly convex upward

Fig. 72.-A, Aspergillus glaucus; B, Fig. 73.-Fungi (penicillium glaucum). aspergillus niger; C, ripe fructiferous

spores.

(columella). The sporangium contains within its interior, separated by septa, the large cylindric-oval spores.

4. The streptothrices form, to a certain degree, a transition between the filamentous fungi and the bacteria. They consist of long, cylindric filaments, dividing by budding, and from which finally a true mycelium is formed. In many of these air-hyphae develop, which simply give off special fruitheads, spores (segmentation). These streptothrix-spores must not be placed upon the same plane as the permanent forms of the bacteria. In older cultures the streptothrixthreads disintegrate into degenerative products resembling bacteria, like rods, cocci, spirilla (fragmentation). If these structures are transplanted upon fresh nutrient material, a

true filamentous network will at once redevelop. The peculiarities of the streptothrices will be referred to in detail in the discussion of actinomycosis.

5. Oidia (segmented molds) are likewise simple in arrangement. They also possess no special fruit-heads, the spores being detached directly from the fruit-bearers that arise from out of the mycelium. Their most frequent representative is the oidium lactis, the white milk-mold, which vegetates upon sour milk. The oidia form a transition to the so-called budding fungi.

The budding fungi or yeast-fungi are chlorophyl-free cells of roundish or oval shape that multiply by budding— that is, a small, roundish, bud-like projection grows from the periphery of the mother-cell and, gradually increasing

in size, assumes the shape of the mothercell, from which it ultimately becomes detached. The newly formed cell undergoes the same process. If the various generations of cells remain attached to one another, long rows of yeast-cells result the so-called strings of buds. Under special nutritive conditions-for instance, upon solid culture-media of alkaline reaction or deficient in sugar-the budding fungi also form true mycelial threads. (See Thrush, p. 351.) The best known of the budding fungi are the yeasts (saccharomyces cerevisiae) and the mold of wine-must (mycoderma vini).

Fig. 74.-Yeast-fungi.

Filamentous and budding fungi flourish at room-temperature. For their nutrition they require constantly preformed organic substances, water, and, further, oxygen as a rule; a number of the filamentous fungi may develop also in the absence of oxygen. Acid culture-media are preferred, although the filamentous and the budding fungi grow also upon alkaline media. These fungi are present everywhere in nature, and are always numerous in the air and upon articles of food. They are capable of inducing fermentation (especially, though not exclusively, the budding fungi) and decomposition. Putrefaction, which is usually of bacterial origin, inhibits the development of filamentous and budding fungi in general.

Microscopic examination for filamentous and budding fungi is made on the whole in the same way as that for

bacteria. The filamentous fungi, with the exception of the streptothrices, which behave exactly as do bacteria with regard to stains, do not stain well in general, although they can be demonstrated with the aid of Löffler's methyleneblue. Generally, it is preferable to examine these fungi unstained. The filamentous fungi do not take up water, so that they are generally mounted in glycerin. It is advisable to undertake the demonstration of teased preparations from fungous vegetations in 50 per cent. alcohol containing a few drops of ammonia, in order to avoid the disturbing influence of air-bubbles; or the teased preparations are made in Unna's solution: gelatin 1, alcohol 25, solution of ammonia 25, glycerin 25, water 35. The following recommendation of Unna is useful: The cover-slip preparations are placed for a minute in 5 per cent. potassium hydroxid; then, after rinsing in water for five minutes, in 5 per cent. acetic acid; and finally they are exposed to the action of a strong aniline stain (for instance, gentian-violet), possibly under the influence of heat. Yeast is best stained with a dilute aqueous solution of vesuvin, as the other aniline dyes readily give rise to overstaining.

The cultivation of molds and budding fungi is carried out in the same way as that of bacteria. Isolation is effected by means of the plate-procedure, preferably with acid gelatin or agar (the gelatin or the agar is dissolved in acid fruit-decoctions, beer-wort, or potato-water (p. 81)), instead of alkaline bouillon. For further cultivation bread-pap is well adapted (p. 86).

PATHOGENIC ACTIVITY OF FILAMENTOUS AND BUDDING FUNGI FOR ANIMALS.

Although the majority of filamentous and budding fungi vegetate only upon dead organic material, a small number of varieties may flourish in the animal body and thus give rise to disease. A special position is occupied by the streptothrices, the most important representative of which, the streptothrix actinomyces (p. 354), will be fully considered. The best known among the remaining pathogenic filamentous fungi are the aspergillus fumigatus and flavescens, and the mucor corymbifer and rhizopodiformis. If an emulsion of these fungi in bouillon is injected into the

ear-vein of a rabbit, the animal will die after the lapse of two or three days in consequence of a general mold-mycosis. In all of the organs, most abundantly in the kidneys and in the liver, small, whitish-gray nodules are present, which, when viewed microscopically, are found to consist of a dense network of mycelial threads. These fungous vegetations never, however, contain fruit-bearers or conidia. Careful investigation has shown that germination of the injected spores has taken place, but that fruit-formation never takes place in the animal organism.

By reason of its deficiency in free oxygen and its alkaline reaction the organism does not constitute a suitable nutrient medium for most molds. The overwhelming majority of these die when introduced into the body, whether through the breath or in any other way. The few varieties that survive at all prove pathogenic only by germinating, and acting as foreign bodies inducing disturbances mechanically through irritation and vascular occlusion, etc. They do not undergo fructification or actual multiplication. Nothing likewise is known with regard to any chemic activity on the part of molds or budding fungi in the body. In a certain sense the mold-mycoses are, accordingly, not true infectious diseases, as they are not attended with multiplication of the exciting agent, and with intoxication. Success in inoculations with pathogenic molds depends, therefore, also upon the number of spores injected. The number of disease-foci corresponds exactly with the number of spores introduced, and the animals die as a result of the extent of the foci of disease alone. The pathogenic molds are, besides, inherently pathogenic, and likewise the nonpathogenic molds are always nonpathogenic. Augmentation or attenuation. of pathogenicity can not be effected. The pathogenic varieties are not equally pathogenic for all animals. Thus, the mucor corymbifer, which destroys rabbits, is harmless in dogs.

Pathogenic molds are quite widely distributed in nature. It is only necessary, for instance, to expose unsterilized. bread-pap in a closed beaker for one or two days to a temperature of from 30° C. (86° F.) to 40° C. (104° F.), in order to see a dark-green fungous coating form, consisting of aspergillus fumigatus. The culture is generally pure, as at a temperature of between 30° C. (86° F.) and 40° C. (104° F.) the aspergillus overgrows all other molds. If,