The Elements of Bacteriological Technique Part 29

2. Drain off the excess of water.

3. Cover the section with diluted Leishman (1 part stain, 2 parts distilled water) and allow to act for five to ten minutes (until tissue appears a deep blue).

4. Decolourise with acetic acid solution until only the nuclei appear blue (examine the section wet, with low power objective).

5. If the eosin colour is too well marked treat with the caustic soda solution until the desired tint is obtained (as seen with the 1/6-inch objective).

6. Wash with distilled water.

7. Rapidly dehydrate with alcohol.

8. Clear with xylol.

9. Mount in xylol balsam.

~VIII. CLa.s.sIFICATION OF FUNGI.~

For practical purposes FUNGI may be divided into:

~1. Hymenomycetes~ (including the mushrooms, etc.).

~2. Hyphomycetes~ (moulds).

~3. Blastomycetes~ (yeasts and torulae).

~4. Schizomycetes~ (bacteria).

NOTE.--Formerly myxomycetes were included in the fungi; they are now recognized as belonging to the animal kingdom, and are termed "mycetozoa."

~MORPHOLOGY OF THE HYPHOMYCETES.~

At the commencement of his studies, the attention of the student is directed to the various non-pathogenic moulds and yeasts, not only that he may gain the necessary technique whilst handling cultivations of harmless organisms, but also because these very species are amongst the commonest of those that may accidentally contaminate his future preparations.

The hyphomycetes are composed of a mycelium of short jointed rods or "hyphae" springing from an axis or germinal tube which develops from the spore. Hyphae are--

(a) Nutritive or submerged.

(b) Reproductive or aerial.

The protoplasm of these cells contains granules, pigment, oil globules, and sometimes crystals of calcium oxalate.

~Reproduction.~--Apical spore formation--as.e.xual; zoospores--s.e.xual.

~Mucorinae.~--_Mucor_ (Fig. 77).--Note the branching filaments--"mycelium"

(a), "hyphae" (b).

Note the as.e.xual reproduction.

1. A filament grows upward. At its apex a septum forms, then a globular swelling appears--"sporagium" (d). This possesses a definite membrane.

2. From the septum grows a club-shaped ma.s.s of protoplasm--"columella"

(c).

[Ill.u.s.tration: FIG. 77.--Mucor mucedo.]

[Ill.u.s.tration: FIG. 78.--Aspergillus]

3. The rest of the contained protoplasm breaks up into "swarm spores"

(e).

Finally the membrane ruptures and spores escape.

~Perisporaceae.~--_Aspergillus_ (Fig. 78).--Note the branching filaments--"mycelium" (a).

[Ill.u.s.tration: FIG. 79.--Penicillium.]

Note the as.e.xual reproduction.

1. A filament (b) grows upward, its termination becomes clubbed; on the clubbed extremity flask-shaped cells appear--"sterigmata" (c).

2. At free end of each sterigma is formed an oval body--a spore or "gonidium" (d), which, when ripe, is thrown off from the sterigma. Two or more gonidia may be supported upon each sterigma.

_Penicillium_ (Fig. 79).--Note the branching filaments--"mycelium" (a) (frequently containing globules).

Note the as.e.xual reproduction.

1. A filament grows upward--"goniodoph.o.r.e" (b)--and its apex divides up into several branches--"basidia" (c).

2. At the apex of each basidium a flask-shaped cell, "sterigma" (d), appears.

3. At the apex of each sterigma appears a row of oval cells--"spores" or "conidia" (e). These, when ripe, are cast off from the sterigmata.

[Ill.u.s.tration: FIG. 80.--Odium.]

~Ascomycetae.~--_Odium_ (Fig. 80).--(This family is perhaps as nearly related to the blastomycetes as it is to the hyphomycetes.)

Note the branching filaments--"pseudomycelium" (a). Here and there filaments are broken up at their ends into oval or rod-shaped segments, "odia," and behave as spores.

Note the as.e.xual reproduction. From the pseudomycelium arise true hyphae (b), each of which in turn ends in a chain of spores (c).

~MORPHOLOGY OF THE BLASTOMYCETES.~

The blastomycetes are composed of spherical or oval cells (8 to 9.5 in diameter), which, when rapidly multiplying by budding, may form a spurious mycelium. A thin cell-wall encloses the granular protoplasm, in which vacuoles and sometimes a nucleus may be noted. This latter is best seen when stained with haematoxylin (see page 105).

During their growth and multiplication the blastomycetes split up solutions containing sugar into alcohol and CO_{2}.