The Sea Shore

by William S. Furneaux

Hitherto we have spoken only of mounting small objects in water, and this is advisable when the object is moist, whether it be animal or vegetable, alive or dead. But dry objects may be examined in the dry state, in which case they need not be covered. If they are composed of transparent material they are to be dealt with in the manner recommended before, as far as the management of the light is considered; that is, a moderately strong light is sent through them by the reflector below the stage; but opaque objects are best examined on a dead black ground, the light being directed on to them by means of a condensing lens placed between them and the source of light.

A collector who has done only a few days’ work on the sea shore will probably find himself the possessor of a host of interesting objects that will afford much pleasure and instruction when placed under the microscope—objects, many of which have been somewhat hastily deposited in a bottle of spirit or other preservative for study in his future leisure moments. These objects, if small, may be examined as above described, simply placing them under a cover-glass, or in a cell, with a clear drop of the same liquid in which they have been kept.

The general characters of the larger objects may also be observed by means of some kind of hand lens, but even these are generally best examined under water or other suitable liquid.

A great deal may be learnt of natural objects by preparing very thin sections for microscopic examination; and although special works should be consulted if one desires to become proficient in the different methods of cutting and preparing such sections, yet a great amount of good work may be done with the aid of a sharp razor, manipulated with nothing more than ordinary skill.

Some objects, especially certain of those of the vegetable world, are of such a nature that suitable sections may be cut, either from the fresh or preserved specimen, without any preliminary preparation. All that is required is to hold the object firmly between the finger and thumb of the left hand, previously securing it in some kind of holder if necessary, and pare off the thinnest possible slices with a horizontal movement of the razor, both razor and object being kept very wet during the process. As the sections are cut they may be allowed to drop into a shallow vessel of water; and, the thinnest then selected for examination in water as previously described.

Other objects are so soft that the cutting of sections becomes impossible without previously hardening them. Methylated spirit is a good hardening reagent, and many of the soft structures that have been preserved in this fluid, especially if it has been used undiluted, will be found sufficiently hard for cutting thin sections. Among the other hardening reagents used by microscopists may be mentioned a solution of chromic acid—one part by weight of the solid acid dissolved in from one hundred to two hundred parts of water, and a solution of bichromate of potash—one part of the bichromate to about forty parts of water. In either case the hardening of the object takes place slowly, and it should be examined from day to day until the necessary consistence has been obtained.

The structures of many soft animals can never be satisfactorily hardened for section-cutting by either of the above reagents, and thus it becomes necessary either to freeze or to imbed them. In the former case the object is first soaked in gum water—a thin solution of gum arabic—and then frozen by an ether spray or by a mixture of ice and salt. The sections should be cut with a razor just as the object is beginning to thaw, and they may then be examined under a cover-glass, in a drop of the gum water.

The other method is conducted as follows:—The soft object is first soaked in absolute alcohol to extract all the water it contains, and is then transferred to paraffin that has been heated just to its melting-point by standing it in warm water. After the object is thoroughly permeated with the paraffin, the whole is cooled quickly by immersion in cold water. Sections are now cut, the paraffin being sliced away with the substance it contains. These sections are placed in warm turpentine, where they are allowed to remain until the whole of the wax has dissolved, and they may then be mounted in a drop of turpentine, and covered with a cover-glass.

We have given brief instructions for temporary mounting only, but most amateur microscopists would undoubtedly prefer mounting their objects permanently, so that they may be set aside for study at any future period. Hence we append a few directions to this end, advising the reader, however, to consult a work dealing especially with this subject if he desires to become proficient in the preparation of microscopic slides.

Moist objects, including those which have been preserved in dilute spirit, may be soaked in water, then transferred direct to the glass slip, and covered with a drop of glycerine. Any excess of the glycerine should then be absorbed from around the cover-glass by means of a strip of blotting-paper, and the edge of the cover cemented by gold size applied with a small camel-hair brush.