strip of mica and then burn them, avoiding the great annoyance of having a cover-glass, diatoms and all, slide or fly off. The mica being thin and a poor conductor of heat, the end may be brought to a red heat almost instantly. Now place a glass slip on the turntable, and make a dot or a small circle in the centre as a guide for placing the diatoms. Turn the marked side down, and with gelatine or other material size the spot over the dot or circle; then with scissors cut from the film of mica a small piece from the best part of the diatom field, moisten the other side and lay it on the glass slide near the marked centre. A crescent-shaped piece may be cut, if desired, that may extend partially around the marked spot. The mica being thin, the focus of low powers need not be changed while transferring the diatoms from the mica to the slide, and one trial will demonstrate that it is much easier to pick from mica than from glass; also that there is less danger of having the mica fall from the slide while at work. Those who desire to make the arrangement on a cover-glass can do so by placing a cover over the marked centre, sizing it, and then transferring to the cover instead of to the slide.

Mounting Diatoms in Series.*-P. Francotte uses Threlfall's method for arranging diatoms in series. The solution of caoutchouc being poured upon the slide, the benzine evaporates, and the diatoms are arranged; it is then slightly heated, and the diatoms sink into the layer of caoutchouc, where they remain definitively fixed, and can be covered with a thin glass coated with balsam.

Synoptical Preparation of Pulverulent Objects (Diatoms from Guano, Fossil Earths, &c.). ‡-P. Barré describes as follows his process of making these preparations, which enable specimens of different pulverulent objects to be compared.

After covering one of the surfaces of a cover-glass with balsam in the manner described for arranging diatoms, § and heating it until the hardened balsam no longer contains any trace of chloroform, the cover-glass is placed in the instrument fig. 42, A. a is a plate of brass, 75 mm. in thickness. b is a strip of steel, fixed at e to the plate a, and to which is riveted another brass plate c. To the latter are soldered nine copper tubes, made as thin as possible (1/5 or 1/6 mm.) These tubes pass through the plate c, and project about 1 mm. from its under surface. The tubes are of exactly the same length, so that the cover-glass, covered with hardened balsam, meets all the nine tubes at once.

The plate a has a rectangular aperture d (indicated by dotted lines), and exactly opposite to the orifices of the nine tubes in the plate c.

The cover-glass is placed between a and the tubes, the surface covered with balsam being in contact with the nine tubes.

This operation complete, a copper or steel wire, or even simply an

*Bull. Soc. Belg. Micr., x. (1884) p. 65.

† See this Journal, iii. (1883) p. 600.

Bull. Soc. Belg. Micr., x. (1883) pp. 16-18 (1 pl.).

§ See this Journal, iii.(1883) p. 453 (1 pl.).

ordinary pin, is introduced transversely between the lower surface of the cover-glass and the square opening (fig. 42, B). This causes the cover-glass to rest with equal pressure on all the nine tubes at once. Thus prepared, the glass, fixed in the instrument, is exposed to

the heat of a spirit-lamp. The balsam is again liquefied, the extremity of the tubes in contact with it become attached, and it is then allowed to cool.

The varieties of powder containing diatoms are then introduced into the tubes by means of a quill, and spread by a fine and very soft brush on the inner surface of each tube. The operation should be performed very carefully, so as not to allow particles of powder to fall into the adjoining tubes. The glass is again heated, and the diatoms adhere to the softened balsam in all the tubes at onceafter which it is again allowed to cool. Then, by raising the spring b, the cover-glass is carefully loosened, and can then be

detached with a slight pressure. The surface of the glass having the diatoms is then blown and brushed, and the preparation is completed by the process described for arranging diatoms.

The essential point of the operation is in sufficiently hardening the balsam on the cover-glass. The heating must be carried as far as is possible without altering the colour. To succeed, it is advisable to cover the spirit-lamp with a metal chimney to avoid the flickering of the flame. This chimney has a cap (g, fig. 42, C and D), movable vertically, so that it can be raised or lowered. It is also convenient to joint it in such a manner that the hot plate can be placed perpendicularly, if desired.

It is, of course, permissible to increase at pleasure the number of tubes. The author makes preparations containing sixteen and even twenty-five varieties of earths; and expects to greatly exceed this number. Indeed, the only limit is the size of the cover-glass.

Logwood Staining.-A. C. Cole says that "up to the present time, no stain has been found to equal logwood for certainty and permanency of results, and beauty of colour, which, besides being beautiful, is also not too tiring for the eye. We go further, and say that the more a histologist departs from a use of logwood and adopts other stains, the more unsatisfactory will be his total results. If ten men were each to make for himself a histological cabinet, the work of each being equal in other ways, the one who would produce the best cabinet would be found to have used logwood and picro-carminate of ammonia for the great majority of his slides, using other stains which have been found to suit special cases, such as aniline-blue-black for nerve-centres, methyl-aniline for amyloid or waxy degenerations in pathological histology in a few cases only. He would further have been found to have used benzole balsam as his mounting medium in the case of his logwood stains, and glycerine jelly for mounting his picro-carmine slides. Such a cabinet would last a thousand years, and be as perfect the last day as on the first. On the other hand, the worst cabinet, especially after, say about ten years, would be found to have been composed of a few logwood slides, mounted in dammar varnish, and the great majority stained with all sorts of aniline and other fancy dyes, and mounted in glycerine. dammar preparations would be found to be little better than fine grey dust, and the fancy dyes to be conspicuous by their absence. So far as can be judged by our present data, a preparation stained with logwood and mounted in balsam is unchangeable; so is a preparation stained with picro-carminate of ammonia and mounted in good glycerine jelly.

The

With these preliminary remarks, we now proceed to give formula for those stains, and those only, which have been found really good in every way. As staining is yet in its infancy, we daily read of a fresh stain, and a new method of staining. We need scarcely draw the attention of our readers to the present mania for 'rushing into print,' and the numerous worthless, not to say senseless, communications to

*The Methods of Microscopical Research,' Part VII. (1884) p. xli.

our various journals on the subject of dyes for histological work. We advise the histologist to ask himself this question: Is it my object to make for myself a complete educative histological cabinet, or to investigate the subject of stains, and therefore to experiment with the various stains? The operator should settle this question once for all, and before he commences his work.”

Staining with Hæmatoxylon.*-Dr. C. L. Mitchell describes a new and simple method of preparing a logwood staining fluid, by which a permanent, reliable, and satisfactory preparation can, he claims, be easily made, and which places within the reach of every microscopist, a staining fluid "stable in composition, comparatively easy of preparation, and unequalled in the delicacy and clearness of differentiation of its colouring."

In staining fluids prepared from extract of logwood, the partially oxydized tannin in the liquid gradually absorbs more oxygen from the air and changes to other complex organic compounds; the colouring matter is also affected by the decomposition, and gradually becomes converted into other substances, and the liquid finally becomes of a dirty muddy colour, and is half filled with a lumpy sediment. This change will be found to take place in all ordinary logwood staining fluids, whether prepared from the extract or from the drug itself, although from the nature of the case those made from the extract would be most quickly affected. The idea therefore occurred to the author, that if the tannin could be removed, and the lake of logwood isolated in a state of comparative purity, a staining fluid could be prepared which might possibly be both permanent and satisfactory, and the following formula is the result of his investigation:

Moisten the ground logwood with sufficient cold water to slightly dampen it, place it in a funnel or percolator, packing it loosely and then percolate sufficient water through the drug until the liquid coming from the percolator is but slightly coloured. Allow the drug to drain thoroughly, and then remove it from the percolator and spread out on a paper or board to dry. Dissolve the alum in eight fluid ounces of water, moisten the dry drug with a sufficient quantity of the fluid and again pack in the percolator, this time rather tightly, and pour on the remainder of the alum solution. As soon as the liquid percolates through and commences to drop from the end of the percolator, close the aperture with a tightly fitting cork and allow the drug to macerate for forty-eight hours. Remove the cork at the expiration of that time, allow the liquid to drain off, and then pour sufficient water upon the drug to percolate through twelve fluid ounces

* Proc. Acad. Nat. Sci. Philad., 1883, pp. 297-300.

altogether. Mix this with the glycerine, filter and place in a closestopped bottle.

In this process nearly all the tannin is removed by percolating the drug with cold water, a menstruum in which the colouring principle is not very soluble, and the subsequent maceration and percolation with the alum solution removes the logwood lake in a state of comparative purity. The glycerine is added simply for its preservative qualities, and this may still be increased by the addition of a few drachms of alcohol to the solution.

The hematin staining fluid thus prepared is a clear heavy fluid of a deep purplish red colour. It will keep its colour for a length of time and deposits no sediment. A sample exhibited by the author had been made for nearly a year, frequently exposed to a strong light and open to the air, but was unchanged. Permanent and beautiful in its colour, which is of a delicate violet hue, clear and sharp in its definition of the different tissues under examination, it will bear use with the very highest powers and it is hoped enables observers to distinguish minute differences of tissue which have hitherto escaped notice.

As to the method of using the fluid, it yields good results when used undiluted, as a quick stain; but the best results are obtained by placing the tissues in a weak solution (ten drops to two fluid drachms) with warm distilled water for about twelve hours. This produces results of surpassing delicacy and beauty.

The

Dry Injection-masses *-The variously coloured gelatine emulsions in common use as injections keep for only a short time, and have, therefore, to be prepared as occasion arises for their use. dry emulsions recommended by Dr. H. Fol are very easily prepared and convenient in use. As they will keep for any length of time they can be prepared in quantities, and will thus be ready for use at any moment.

Carmine Emulsion.-One kilogramme gelatine (softer kind used in photography), soaked in water for a few hours until thoroughly softened; after turning off the water, heat the gelatine over a water bath until liquefied, and then add to it, little by little, one litre of a strong solution of carmine in ammonia. The mixture, stiffened by cooling, is cut up, and the pieces packed in a fine piece of netting, Vigorous pressure with the hand under water forces the emulsion through the net in the form of fine strings or vermicelli. These strings are placed in a sieve and washed until they are free from acid or excess of ammonia; then collected and re-dissolved by heating. The liquid is poured upon large sheets of parchment which have been saturated with paraffin, and these sheets are then hung up to dry in an airy place. The dried layers of the emulsion, which are easily separated from the parchment, may be cut into strips and placed where they are protected from dust and dampness.

The carmine solution used in this emulsion is prepared as

Zeitschr. f. Wiss. Zool., xxxviii. (1883) pp. 492-5. Cf. Amer. Natural., xviii. (1884) pp. 219–20.