and may then be placed under the microscope in oil of cloves. Thus the whole process does not take more than ten minutes.

The sections are not only quickly but well stained, and indeed, as I have found by comparing results, for the most part better even than when submitted to the slow action of the carmine.

I have, however, only treated sections of the central nerve system (brain and spinal marrow of man and animals) by this method, but it ought to be applicable to other structures. It is, of course, understood that the previous preservation and hardening of the preparation must be well done in order to obtain a corresponding staining. For fresh preparations or for preparations in alcohol (which latter are generally to be avoided as much as possible with the central nerve system), this method does not answer; objects colour best which have been hardened in chromate of potash (especially with the addition of a few drops of chromic acid).

Moderate heating does not hurt the preparation; the precipitate of carmine, which might be thrown down by it, may readily be avoided. A neutral ammoniacal solution of carmine, not too concentrated, furnishes all that can be desired.

It is not only on account of its rapidity that I now generally adopt this method, there is in addition the advantage that the preparations thus treated are coloured in a specially sharp and distinct manner; for example, the connective-tissue corpuscles, together with their long continuations into the substance of the brain, which insert themselves in the adventitia of the vessels, come out with a distinctness which it is difficult to obtain by other means.

*

A New Field for the Microscopist (the Flagellate Protozoa).— In the April number of the 'Popular Science Review,' Mr. Saville Kent, after referring to the improvements which have been made by opticians, in this and other countries, in the construction of object-glasses, and suggesting that "it would be a matter for congratulation if we could place on record side by side with this attestation to the mechanical perfection and improvements of our magnifying instruments, evidence of an equivalent amount of progress achieved by microscopic workers in those new fields for investigation thrown open to them by the skill of the optician," proceeds to give a descriptive outline, with illustrations, of certain of the Flagellate Protozoa-"an extensive series of forms that have so far, on account of their exceedingly minute size, altogether evaded the notice of the microscopists of this country, but which at the same time most certainly surpass all previously discovered types, equally in the wonderful symmetry of their individual form and in that of their aggregated mode of growth, requiring for their satisfactory interpretation the employment of the most powerful and high-class magnifying powers."

It is impossible within the limits of a "Note" to give any intelligible abstract of Mr. Kent's detailed description of some of the forms, for which the paper itself must be referred to. Some of them are described and figured in a paper read by the author before the Royal Microscopical Society, and printed in the Transactions' for January 1872.

The close relationship which, as Mr. Kent considers, undoubtedly * Dr. H. Obersteiner, in Archiv f. Mikroskopische Anatomie,' xv. 1.

subsists between the sponges and the extensive group of independent collar-bearing Flagellate Protozoa, is discussed at some length; and while recommending these organisms to the attention of working microscopists, it is pointed out that it is much to be desired that they should supplement their observations by a practical examination of the structure of all such sponge forms in the living state to which they may have access. In either field our knowledge may be said as yet to extend no farther than the threshold, and in each of the same there is probably more original discovery waiting to be achieved than in any other group of the organic world.

Mr. Kent gives the following hints as to finding these interesting forms. Either salt or fresh water will be found to yield its quota; those frequenting the last-named element being usually the more accessible, will most probably command first notice. The investigator should procure from the nearest weedy ditch or pond a bottleful of the finely divided leaves of Myriophyllum, or of tangled confervoid growths, in either case selecting more especially those brownhued specimens coloured by a dense incrustation of other more minute vegetable and animal parasitic growths. Care should be taken to enclose with the water as large a number as possible of the specimens of Cyclops and other Entomostraca, to which will frequently be found attached species rarely, if ever, to be met with elsewhere. Patiently exploring every filamentous division of the weeds with a power of 900 diameters, it will be scarcely possible to miss encountering one or more of the species, which with so low a power will appear as mere luminous specks, and will require a power of 2000 diameters for their proper identification.

The Royal Microscopical Society of the Sandwich Islands.-King Kalakua has recently established in his dominions a Society under the above title; particulars of its constitution and operations are on their way to this country. The king has always given active encouragement to science, and in his honour a new fungus, lately discovered growing on a boat thrown up on the beach near Honolulu, has been named (by Mr. J. P. Moore, of San Francisco) Polyporus Kalakua.

Count Castracane on Diatoms.-At a sitting of the Botanical Society of France last summer, Count Castracane exhibited more than 2000 photographs of diatoms magnified 535 diameters, and stated that his entire collection contained about 3000, of which the negatives were carefully preserved. He described his mode of ascertaining the number of striæ in a given space. He projects the image of a millimetre divided into 100 parts, so that the enlargement of each Tổ of the millimetre occupies a space on paper of 18 centimetres. Taking," he says, a power of this measure, I superpose an image of the diatom, selecting the clearest part, and then determine with certainty and without fatigue the number of stria that correspond with the space of inch.”

66

66

His measurements led him to deny that Navicula crassinervis, N. rhomboidea Ehr., and Frustulia Saxonica Raben., belong to the same species. He exclaims," How could I believe this, when I am assured that in N. rhomboidea Ehr. the longitudinal divisions, or, more correctly, the intervals between its rows of granules in the

longitudinal direction, are smaller than those between the transverse rows, while in N. crassinervis the opposite is observed, and the transverse intervals are much narrower than the longitudinal ones."

Referring to the use of monochromatic light by Amici, he stated that he used "a prism of 35° of flint glass, in which the solar ray is decomposed in immersion and emersion," and that a Paris optician was going to make a cheap and suitable heliostat. He usually employed the blue, or green, or extreme violet rays, but practice was necessary with the latter to get used to the demi-obscurity.*

The New Oil-immersion Object-glass.-The Rev. W. H. Dallinger writes to 'Nature' :-"As a piece of workmanship this lens is extremely fine; and it can be used with quite as much ease as an ordinary immersion inch objective. It works admirably with Powell and Lealand's ordinary sub-stage condenser, with Wenham's reflex illuminator, and with the small plano-convex lens which the maker sends with it to be fastened to the under surface of the slide with the oil of cedar wood. But I have also secured admirable results with the illuminating lens of Powell and Lealand's supplementary stage, which gives entire command over the angle of the illuminating ray.

"The spherical aberration is beautifully corrected, the field being perfectly flat. The colour corrections are, so far as the lens goes, equally perfect; but are somewhat conditioned by the dispersive power of the oil, which can be modified readily. The sharpness and brilliance of the definition which this lens yields is absolutely unsurpassed, in my experience; and it has a very great power of penetration.

"I tested it with a series of tests with which I have proved and compared the glasses of various makers in England, the Continent, and America for some years. Up to the time of receiving this lens, the 1-inch that had done the most in my hands, was one of the 'new formula' lenses of Powell and Lealand. It is but justice to say that all my most crucial tests were equally mastered by the lens of Zeiss. I have not been able to do more with it than with the English glass, but the same results can be accomplished much more readily. The correction has to be brought into operation, and careful adjustment made, to get the finest result with the English lens; but the German glass has simply to be brought into focus, and the best result is before the observer, provided that the light has been adjusted in the most efficient manner. It is true that for sharp and perfect definition we must be careful to adjust the length of the draw-tube; in working this lens there is much need of attention to this matter; and speaking from a practical point of view, it takes the place, in securing crisp definition, of the screw-collar adjustment, although, of course, much easier of application. But it is so easy to work the lens with fine results on the more delicate tests, that I think that those who make the resolution of these their primary object in the possession of a microscope, can scarcely fail in securing their utmost desire. It is a glass pre-eminently suited for the resolution of difficult lined or beaded objects.

"Amphipleura pellucida is easily resolved into delicate beads when the frustules are moderately coarse; and almost any that can be met with are resolvable into lines; and this when these diatoms are

*Bulletin de la Soc. Botanique de France,' t. xxiv., 1877.

mounted in balsam. The highest eye-pieces made may be used without any practical detriment to the image, although, of course, with a reduced sharpness of the definition.

"On the whole, I think it in many cases the finest lens, of its power, that I have ever seen; and in every sense it is an admirable acquisition."

In conclusion, Mr. Dallinger refers to "another feature in the use of this lens which is a drawback," viz. that the oil is a solvent of most varnishes and gums used in mounting and finishing slides (which may be remedied by coating the edge of the cover with shellac varnish); and also to the necessity for the objects, such as frustules of diatoms, to be "burnt" on to the cover or mounted in balsam or other fluid with an equal refractive index.

Dry v. Immersion Objectives.—In the same letter Mr. Dallinger observes :- "Even water immersion lenses are of very limited service in observations continuously conducted upon minute living organisms in fluid. We may gladly call in their aid, in the determination of a delicate change of form, or in the more perfect detection and definition, of an obscure point of structure; but for steady and constant work we are bound to avoid them; for the fluid under the delicate cover is in danger every moment of being 'flooded' by coming into contact with the water on the top of the cover, and between it and the lens; because the movements of the organism have to be counteracted by the movements of the mechanical stage, in order to keep any form that may be studied in view constantly. But this opens to us the possibility of going to the edge of the cover at any moment; and thus, by the mingling of the fluids, rendering the observation void. This, of course, will apply still more fully when, as in the case of the valuable glass of Zeiss, the 'immersion fluid' is an essential oil.

"Happily it is only in special cases that the greater analyzing power, combined with larger working distance, which is possessed by immersion lenses, is required. It is in the earlier study of an organism, and before continuous work upon it has begun. And even if it be not, in the majority of cases a first-class dry English lens of a higher magnifying power, if efficiently used, accomplishes all that is required. Hence the fine new formula' lenses, dry (also provided with fronts to be used as immersion lenses), are as yet an unsurpassed boon for this special class of work. And certainly it is one which, in relation to biology, has a most important future. I know, of course, that the optician has irresistible limitations to deal with; but the new formula' dry lenses I have referred to, prove, in comparison with the preceding lenses, made by the same firm, that the dry lens was capable of most serviceable improvement. What is important, therefore, is that the larger demand for lenses that will resolve readily, difficult lined and beaded objects, which can certainly be best done, all things being equal, with immersion lenses--and to the improved manufacture of which Zeiss' oil immersion gives apparently a new departure should not lead the best opticians in England, the Continent, and America to abandon efforts for the still greater improvement of their dry lenses. They are of the greatest value to the practical biologist, working amidst the minutest living things in nature, and from the study of which so much may be anticipated."

BIBLIOGRAPHY.

1

The first part of Professor Ranvier's 'Traité technique d'Histologie' has been issued. An English translation is in preparation. The ANNALS AND MAGAZINE OF NATURAL HISTORY for May:— Notes on the Genus Retepora, with Descriptions of New Species. By the Rev. Thomas Hincks, B.A., F.R.S. (With 2 plates.)

Emendatory Description of Purisiphonia Clarkei, Bk., a Hexactinellid Fossil Sponge from N.W. Australia. By H. J. Carter, F.R.S., &c.

On Calcareous Hexactinellid Structure in the Devonian Limestone; large Fossil Hydrozoic Coralla from the Chalk; and further Observations on the Replacement of Silex by Calcite. By H. J. Carter, F.R.S., &c.

Minor notes:

On Selaginopsis, Polyserias, and Pericladium. By M. C. Mereschkowsky. And on the Rhizopoda of the Salt Lake of Szamosfalva. By Dr. Geta Entz.

For June:

On the Reticularian and Radiolarian Rhizopoda (Foraminifera and Polycystina) of the North Polar Expedition of 1875-76. By Henry B. Brady, F.R.S. (With 2 plates.)

HARDWICKE'S SCIENCE-GOSSIP for May:

What a Diatom is (translated from the paper by M. Julien Deby, in the Bulletin of the Belgian Microscopical Society). (With 5 woodcuts.) A Wet Method of Preparing Objects for Microscopical Mounting. By Mr. A. W. Stokes. -A New (Oil) Immersion Object-glass.-Marine Amoeba.-Kent's 'New Field for the Microscope.'-Fossil Diatomaceæ, &c.-Diatomaceous Deposits near Richmond.—Mr. Thomas Bolton's Living Microscopic Organisms.—Professor J. E. Smith's Apology for Diatomaniacs.

For June:

What a Diatom is (continued). (With 3 woodcuts.)-A Glass-Eating Lichen. By H. T. Johnston-Lavis. (With 4 woodcuts.)-On Preparing and Mounting Leaves and other parts of Plants to show the Crystals in situ. By W. H. Hammond." Cutting it fine" (33 sections of the head of one cockroach, made by Mr. E. T. Newton).-Fossil Diatomaceæ.-Aquaria for Microscopic Work.— Small Aquarium for Microscopic Objects.-Canada Balsam in India.-The Hackney Microscopical Society.-Fossil Fresh-water Sponges (in the so-called "Flints" "found in the Purbeck Limestones).-Removing Surplus Balsam.

GREVILLEA for March :

Reproduction of the Ascomycetes (conclusion). By Dr. Maxime Cornu.

For June:

British Bog-Mosses. (Rev. J. C. Vize's Microscopical preparations of Dr. Braithwaite's series of Sphagnum specimens.)

The Salmon Disease (Saprolegnia ferax). (With 3 woodcuts.)

NATURE for May 16:

The New "Oil Immersion " Object-glass, constructed by Carl Zeiss, of Jena. By Rev. W. H. Dallinger, F.R.M.S.

For May 23:

The Life-History of a Septic Organism. Abstract of paper read before the Royal Society by the Rev. W. H. Dallinger, F.R.M.S.

The PROCEEDINGS OF THE ROYAL SOCIETY for January and February (No. 185):

Observations on the Nervous System of Aurelia aurita. By E. A. Schafer. The Cortical Lamination of the Motor Area of the Brain. By Bevan Lewis, F.R.M.S., and Henry Clarke, L.R.C.P. (With 3 plates.)

Further Researches on the Minute Structure of the Thyroid Gland. Preliminary Communication. By E. Cresswell Baber, M.B. London.

On Schulze's Mode of Intercepting the Germinal Matter of the Air. By John Tyndall, F.R.S.