Collection of Objects.
Infusorial Life, with all its fascinations, was fully unveiled to naturalists by the celebrated Ehrenberg. It was he who termed it infusorial, because he first met with the more interesting forms of minute life in infusions of hay and other vegetable substances. Since his day it is a well-known experience of those who take up the microscope that the most interesting objects to commence with are infusorial living creatures of sufficient dimensions to be easily understood and seen with moderate magnifying powers. Moreover, infusoria are more readily found in almost any pool or running stream of water, either near the surface or clinging to the under surfaces of aquatic plants. At one time all the small shallow pools in the neighbourhood of London—Hampstead Heath, Clapham, Wandsworth, and other commons—abounded in the most interesting forms of life, were famous hunting grounds for the marvellous volvox, the charming dismid and diatom, the wonderful budding and self-dividing hydra. A few hours’ ramble furnished the microscopist with a bountiful supply of these and many other forms of life. Now all is changed; our commons have been devoted to other purposes, and with the general levelling up all the little pools have disappeared, and the microscopist has been warned off and driven further afield, or seeks the good offices of a country friend for an occasional peep into pond life.[48]
A teaspoonful, however, judiciously taken from a well-chosen locality will often be found to contain a variety of living forms, every one of which will deserve a careful and patient study.
Of the microscopic organisms, the collection of which requires no other methods than those ordinarily pursued by the naturalist, most of them must be sought for in pools or running waters, basking in the sunshine, clinging to leaves and rootlets of all aquatic plants; some freely moving about, others clinging to stones or pieces of wood at the bottom. Dismids congregate in shallow waters or rise to the surface in a quiet nook, while the diatomaceæ are seen covering the bottom of clear water, to which they give a yellowish-brown tinge of colour.
Infusorial animal life, as vorticellæ, stentors, rotifers, and various polyzoa, cling, as also do hydra, in colonies to vallisneria, duck-weed, frogbit, or small branches dipping down under water; and if some of the water-weed is brought home the little creatures will live and thrive for several weeks. No waters, however, are so full of minute animal life as the sphagnum bog. A number of species of diatoms, as well as protozoids and the smaller molluscs, will be found in all peat bogs. It is remarkable, too, that the same species, everywhere, are associated with this kind of moss. Lord Sidney Godolphin Osborn supplied his friends with moss growing in a damp part of the garden walk of his rectory; this always furnished the same species of rotifers. These proved to be most interesting objects to my friends, and in an early communication I described them as indestructible, since they will bear any amount of desiccation; nevertheless, they were revived when a drop of water was introduced into the glass-cell.
Fig. 266.—Collecting Stick, Bottle, Hook, and Net.
The Thames mud always furnishes a number of beautiful forms of triceratum. Lower down the river, as brackish water is reached, greater varieties of diatoms appear. But to secure them the collector must be provided with a collecting stick. A convenient form is furnished by Messrs. Baker ([Fig. 266]). This consists of an ordinary walking-stick, together with a lengthening rod, a cutting hook to clear away weeds, ringed bottles with screw tops, and a net with a glass tube attached. Their uses are too obvious to need further description.
The siliceous skeletons of diatoms are met with in the fossil state. Among the first discovered of the infusorial strata were the polishing slates of Bilin and Tripoli, the berg-mehl or mountain meal, the entire mass of which is composed of the siliceous skeletons of different species of diatoms. Richmond, Virginia, is rich in the same organisms, while the great mass of our chalk cliffs are composed of foraminiferous shells, xanthidiæ, &c. One remarkable fact in connection with fossil infusoria is that most of the forms are still found in the recent state. The beautiful engine-turned discs, Coscinodisci, so abundant in the Richmond earth, may be met with in our own seas, and in great profusion in the deposits of guano on the African and American coasts, and in the stomachs of the oyster, scallop, and other salt-water molluscous animals common to our shores.
A great number of infusorial earths may be mounted as dry objects, while others require careful washing and digesting in appropriate media. The finer portions of the sediments will be found to contain the better and more perfect siliceous shells.
Preparing and Mounting Apparatus.
Fig. 267.—Mounting Apparatus.
1.—Ross’s instrument for cutting thin covering-glass for objects. This apparatus consists of a bent arm supporting the cutting portion of this apparatus, which consists of a vertical rod with a soft cork at one end. A brass arm at right angles carries the diamond parallel with and close to the main rod.
2.—Covering-glass measurer. To measure the thickness of covering-glass, place it between the brass plate and the steel bearing; the long end of the lever will then indicate the thickness on the scale, to 1⁄50-th, 1⁄100-th, or 1⁄1000-th inch.
3.—Brass table on folding legs, with lamp for mounting objects.
4.—Whirling table with eccentric adjustment for making cells and finishing off slides.
5.—Air-pump with glass receiver, 3½-inch brass plate for mounting objects and withdrawing air-bubbles.
6.—Improved table with knife for cutting soft sections. This consists of an absolutely flat brass table, with a square hole to receive the wood, or other matter, on a movable screw, which adjusts the thickness of the section.
7.—Smith’s holder with spring and screw for adjusting pressure when mounting objects.
8.—Cutting diamonds for cell-making and cutting slips of glass.
9.—Writing diamonds for cutting thin covering-glass and naming objects.
10.—Page’s wooden forceps, for holding glass slips or objects when heated, during mounting.