1. Ærobic fungi caught over a sewer; 2. Fragments of Penicillium spores; 3. Ærobic fungi taken in the time of the cholera visitation, 1854.
With reference to the ærobic bacteria I have only to add that in addition to the simple mode of taking them on glass slides smeared over with glycerine, special forms of æroscopes are now in use for the purpose, consisting of a small cylinder in which a current of air is produced by an aspirator and diffused through a glass vessel containing a sterilised fluid. These are in constant use in all bacteriological laboratories. The results obtained are transferred to sterilised flasks or tubes as those shown in a former chapter.
Miquel, who has given considerable attention to the subject of ærobic and anærobic bacteria, reckons that the number of spores that find their way into the human system by respiration, even should health be perfectly sound, may be estimated at 300,000 a day.
One of the most commonly met with forms of micro-organisms is Leptothrix buccalis. It chiefly finds its nutritive material in the interstices of the teeth, and is composed of short rods and tufted stems of vigorous growth, to which the name of Bacillus subtilis has been given ([Fig. 282]). Among numerous other fungoid bodies discovered in the mouth, Sarcinæ have been found. See [Plate IX]., No. 7.
Fig. 282.—Section of the Mucous Membrane of the Mouth, × 350.
Showing: a. The denser connective tissue; b. Teased out tissue; c. Muscular fibre; d. Leptothrix buccalis, together with minute forms of bacteria and micrococci; e. Ascomycetes and starch granules.
The Beggiatoa, a sewage fungus, found by me in the river Lea water of 1884 growing in great profusion, consists chiefly of mycelial threads and a number of globular, highly refractive bodies, and may be regarded as evidence of the presence in the water of an abnormal amount of sulphates which set free a gas, sulphuretted hydrogen, of a dangerous and offensive character. Another curious body closely allied to Beggiatoa alba is Cladothrix; this assumes a whitish pellicle on the surface of putrefying liquids.
These saprophytes obtain nourishment from organic matter; nevertheless they are not true parasites in the first stage of their existence, during which they live freely in the water or in damp soil; they, however, become pathogenic parasites when they penetrate into the tissues of animals, and necessarily live at the expense of their host.
Fungi, Algæ, Lichens, etc.