X.
A few words may be said, in the first place, as to the outfit. A very useful part of it is a walking-stick, to which can be attached either a net for capturing the larger forms of life, or a hook for collecting the weeds, to which many forms of great interest and beauty are attached (Fig. [15]). The stick is telescopic, and can also have attached to it a bottle, which, put into the water at any desired spot,—say, amongst a clump of weeds, or near the bottom, upside down, and then suddenly reversed,—will bring away samples of the inhabitants of the neighbourhood. When these are sparsely distributed through the water, the latter may be concentrated by the use of a bottle round the neck of which is firmly tied a coarse calico bag, funnel-shaped, and supported by a wire ring, somewhat as shown in the illustration. Muslin is, however, too coarse for many organisms. This net is immersed in the water so that the ring is just above the surface, and one bottleful after another poured through. The water strains off, the organisms are left behind. The immersion is necessary to reduce the pressure to which delicate organisms would otherwise be subjected. When the bottle is full, or sufficiently concentrated as to its contents, the latter are poured into one of the ordinary collecting-bottles, of which half a dozen at least should always be taken.
Fig. 15.
On reaching home, and as often as possible on the way, the corks should be removed, as these organisms soon use up the air in the water.
For examination a glass trough of considerable size, say three inches in length, half an inch in depth, and two inches in height, should be half filled with the water, and examined with the pocket magnifier. With a little practice it will be found easy to take up not only the larger organisms, but even very minute ones, with one of the dipping-tubes with a long tapering point already referred to. The organism, when “spotted,” is followed by eye and tube, the finger being held over the mouth of the latter, and at the critical moment the finger is removed, and the organism swept into the tube by the in-rushing water. Now wipe off the excess with a clean handkerchief, “spot” the organism in the tube again, and carefully absorb the superfluous water with a piece of blotting paper; and finally, gently but sharply blow the remainder on to the plate of the live-box, put on the cover, and examine with a one-inch power. If, as often happens, the organism sticks to the side of the tube, a little more water must be drawn in, and the process repeated. The use of the cotton-wool trap spoken of previously will often be very helpful in the examination of actively moving organisms.