MICROSCOPY.
Pollen Grains of Cedar.—I have a small quantity of the Pollen of the Cedar of Lebanon (Cedrus Libani), which forms an interesting object for the microscope. I shall by happy to dole out my little stock, as far as it will go, to any who like to send me a stamped envelope. W. H. G., 19, Claremont Square, N.
Balsam and Chloroform.—(In answer to W. G.) This liquid is very convenient in some cases; as air-bubbles are much more easily got rid of than when undiluted Canada balsam is used. It also dries readily, as the chloroform evaporates very quickly, for which reason it must be preserved in a closely-stoppered bottle. It has been said that this mixture becomes cloudy with long keeping, but I have not found it so in any cases where I have used it. Should it, however, become so, a little heat will readily dispel the opacity.—Davies on Mounting Microscopic Objects.
Air-Bladders of Fish.—The following account of a microscopical observation may possibly be new to some of the readers of the Science-Gossip.—In preparing some fish which had been angled the previous day, the air-bladders being unusually large were preserved, and as they promised to be of microscopical interest they were submitted to the instrument. In the blood-vessels interlacing them the corpuscles were observed to be still in active circulation after a period of some fifteen hours of their being caught—an instance of the extraordinary vitality of the life principle. Similar observations may facilitate the investigation of this wondrous and novel spectacle to the young microscopist. The fish, I have subsequently understood, were perch, a species unusually tenacious of life, and predatory in their habitats.—T. R.
Ascertaining the Magnifying Power of Glasses.—(In reply to T. O.)—The apparatus requisite consists of a micrometer slide graduated into thousandths of an inch, each tenth division being marked by a longer line; or two separate slides, one graduated into thousandths, the other into hundredths of an inch; and an ivory scale graduated into inches, tenths, and hundredths. The simplest method is that by double-sight, as it is called. The micrometer slide is placed upon the stage, the lines brought into focus, and the image of one of the interspaces, as seen upon the stage with the open eye, not used in looking through the microscope, is measured with compasses. By then dividing the measure of the image of the space by the known measure of the unmagnified space, the quotient is the required magnifying power. Thus, if the space on the micrometer scale is equal to the 1-100th of an inch, and the image of the magnified space corresponds to 5-10ths of an inch, the space is magnified 50 times: ÷=50.—Micrographical Dictionary.
Formaninifera.—It is now well known that from common chalk it is an easy matter to obtain interesting specimens of Foraminifera. Scrape a small quantity of chalk it is an easy matter to obtain interesting specimens of Foraminifera. Scrape a small quantity of chalk from the mass and shake it in water; leave this a few minutes, pour the water away and add a fresh quantity, shake up as before, and repeat two or three times. Take a little of the residue, and spread it upon the slide, and when quite dry add a little turpentine. When viewed with a power of 250 diameters this will generally show the organisms very well. If it is desired to preserve the slides, they may be then be mounted in Canada balsam. Mr. Guyon observes that the accumulation of the powder, by the action of the rain or exposure to the atmospheric action, at the foot or any projection of the chalk cliffs, will afford us better specimens than that which is "scraped," as the organisms are less broken in the former. When the Foraminifera are of a larger size, though transparent enough to be mounted in balsam, the air must be first expelled from the interior, otherwise the objects will be altogether unsatisfactory. To accomplish this they must be immersed in turpentine and submitted to the action of the air-pump. So difficult is it to get rid of this enemy that it is often necessary to employ three or four exhaustions, leaving them for some time under each. When all air has given place to the turpentine, they must be mounted in the ordinary way.—Davies on Microscopic Objects.
On Collecting Objects for the Microscope.—The following will be found, on an excursion, a useful addition to the collector's stock of wide-necked bottles. Take the smallest sized japanned sandwich-box, about four or five inches long, and a quantity of waste paper—old envelopes, and letters torn so that when folded across the pieces will go easily into the box. On arriving at a likely spot by the side of a pool or ditch, a sample of the produce, whether conferva, bit of rotten stick, or what not, is placed between the folds of one of the bits of waste paper and consigned to the box, the process being repeated as often as agreeable during the ramble. On returning home, the first thing to be done is to transfer the contents of the papers to glasses or jars of water, leaving them till next morning, when the observer's game will be found in excellent order, and ready for the live box or glass slide. The writer has no wish to disparage the bottling system; a well-cooked wide-necked bottle is undoubtedly the best thing, but half-a-dozen such bottles are rather cumbrous, and are soon filled in a productive locality. When this happens, the hunter would be glad to be able to go on collecting and storing in a space no larger than a pocket-book from twelve to twenty good gatherings. Even the most fragile and delicate microscopic forms may be thus brought home uninjured—Volvox, Vorticella, Rotifers, Entomostraca, and, in fact, all the various classes of organisms sought for by those who practise this branch of fishery. Those who desire to command a more extensive range than is afforded by the invaluable hook-ended walking-stick are generally told to provide themselves with a cheap fishing-rod. A much better thing is the handle of an angler's landing-net. These instruments may be had at the fishing-tackle shops, with two or three lengths sliding one within the other like the draws of a telescope, and from their construction, the lengths cannot separate when dragging to land a heavy mass of weeds, as the joints of a fishing-rod are apt to do.—Robert C. Douglas.
British Salmon.—Dr. A. Günther is engaged in a revision of the British Salmonidæ, and, from the materials already at his command, is enabled to affirm that we have at least four non-migratory species which have not hitherto been recognized—one found in the mountain lochs of Wales, one in Ireland, one in the lakes of the Orkneys, and one in the Frith of Forth.
