to Schwarz, who advised the mixing of picric acid with carmine in studying the unstriated muscles of the intestines, or to the picro-carminate of Ranvier, now so well known. I may add also that it has been suggested that a green stain might be obtained with picric acid dissolved in glycerine by the addition of a certain quantity of a decoction of logwood and the neutral chromate of potash, in the proportion of 1 part to 1000.

I avail myself, however, of picric acid mixed with soluble aniline blue to obtain a green tint of considerable delicacy, homogeneous as far as the eye can detect, and which serves to bring out in relief the smallest details which are presented by the tissues and their elements. This green stain is easily obtained, in a comparatively short time, either by subjecting the preparation to be stained to a solution in water of soluble aniline and picric acid, or first to a solution of aniline and then to another of picric acid. In whichever way these colouring matters are employed, an effect is obtained equally quick and satisfactory. The solutions, whether of picric acid or aniline, ought to be saturated, which can be done without difficulty by leaving an excess of each substance at the bottom of the vessels in which the materials are placed to dissolve. In this way we are always sure of employing only saturated solutions. When it is wished to make use of the picroaniline solution, 100 cubic centimetres, for example, should be taken of the saturated aqueous solution of picric acid, and into it should be poured 4 or 5 cubic centim. of the blue liquid also saturated. The resulting solution admirably stains a preparation of the lymphatic glandular system in the space of a few minutes. If it is desired to employ the two substances separately, keep the preparation in the aniline solution for a few minutes, and afterwards place it in the picric acid. In working thus we can see that the preparation is not stained too much by the aniline, and to this end it is well to take it out as soon as it has acquired a light sky-blue tint. By taking it out at this point one is always sure that it will show the nuclear elements sufficiently coloured, whilst the protoplasmic parts and others will be only very slightly stained. By waiting, on the contrary, till the preparation has taken a dark blue tint, the nuclei will be very deeply stained and the other parts rather deeply also, so much so that on submitting it afterwards to the staining action of the picric acid it becomes confused and obscure. The preparations which have been treated with the aniline solution, with the precautions indicated above, and then placed in picric acid, pass in the course of about fifteen minutes from sky blue to a delicate green. After this treatment the tissues show the nuclei both free and cellular sufficiently stained with green, the protoplasm and the fibres coloured pea-green, though faintly and with a delicate shade. Since the staining by the aniline produced by the first treatment was less in these parts, the yellow colour predominates over the blue, whence there results a lighter and more delicate tint.

Similar results are obtained by making a picro-aniline solution act on the different tissues. It is possible to stain with great advantage not only fresh tissues, but also such as have been subjected to the action

of different hardening reagents, such as alcohol, chromic acid, bichromate of potash, &c.

Microscopical preparations obtained by these processes may be preserved like others in fluids or balsam. It should be observed, however, that picric acid, being, as I have said, soluble in water and in alcohol, might easily be removed from the preparations upon which it has been made to act. To prevent this inconvenience it is important that the glycerine used to preserve the preparations should be slightly tinged with picric acid, and if balsam is used it is necessary to dehydrate the preparations in alcohol containing also a small quantity of the same acid in solution. In the latter case, after this treatment, the preparation may at once be placed in oil of cloves or turpentine without fear of the staining suffering from it. I would likewise observe here that if it is intended from the first to mount the preparation in balsam, the operation may be abridged by transferring the preparation immediately from the solution of aniline blue, in which it has acquired the tint I have indicated above, to a bath of alcohol to dehydrate it, the alcohol containing per cent. of picric acid in solution.

With the picro-aniline solution not only may different tissues be stained according to the ordinary process, i. e. by plunging the preparation into it, but interstitial injections may be made with it, and small artificial cedemata produced with Pravaz's syringe. By operating thus, for example, on a lymphatic gland, the colouring matter can be made to penetrate into the cavernous system where the endothelial cellules may be recognized lightly coloured with green, the characteristics of which, already well described by Professor Bizzorero, are seen with more clearness than with any other reagent. If a small cedema be produced under the skin of the groin in a rabbit or guineapig, the connective cellules and the fibres between which they are situated may be studied to perfection, as Renaut has done, by means of eosine, which is soluble in water. The picro-aniline solution, finally, may be very well employed in interstitial injections intended to show the relation between the cellule connectives, especially when the picric acid instead of being dissolved in water is dissolved in one-third part of alcohol.

The preparations thus obtained are not affected by the weak acids, acetic phenic, diluted chlorohydric &c., whilst alkaline solutions rapidly destroy their beautiful outline. The preparations, mounted in fluids or dry, with the precautions mentioned, preserve their stain for a very long time, for I have some which have undergone no alteration for more than a year.

The picro-aniline solution (which is specially to be recommended for the study of the lymphatic glandular system and for the retina) does also very well for other normal or pathological tissues. Thus I have preserved some complete sections of the medulla oblongata stained by this method, which for clearness and elegance leave nothing to be envied in those produced by carmine.

Amplifiers.—In an article on the " Amplifier," by Dr. Devron, in the American Journal of Microscopy,' he says:-" "The Tolles' amplifier used on a large compound microscope, with lenses of various makers, of

', ', and 2, caused resolutions on the Nobert 19th band-plate, which without it at the same time and with the same illumination could not be seen with the same objectives; with that increased resolution the loss of light was not appreciable. Its value was made quite apparent by two photographs showing the resolution of Amphipleura pellucida, one by a and the other by a objective, the latter with the amplifier. The resolution into transverse striæ in both photographs and their appearance is so similar, that were they not numbered I could not tell which was obtained by the objective."

Penetration. The following note from 'Le Microscope,' by Dr. J. Pelletan, p. 55, states a fact that is generally unknown, but which ought to be known to everyone who works with the microscope: "From a purely theoretical point of view an objective with penetration is in reality a defective objective." My experience is that there is not one in a thousand of the users of the instrument-especially the histologists-but have the idea, and their opinions are governed by that idea, that an objective that will show at one sight (or focussing) all the strata or planes in a section of a tissue or of an inch thick, or, in other words, one that has great penetrating power (better defined by the optician's term, "depth of focus "), must be the best and most important objective that can be made. Whereas it can be demonstrated that such depth of focus is optically incompatible with the best definition, which is the quality above all others desirable in a lens.

Depth of focus is a quality desirable in certain cases and for some purposes; the objectives for such use should be made expressly for that property, and the purchasers of such ought not to expect them to be capable of the higher histological work of modern microscopy.

There is, of course, a wide difference in definition of objectives that possess depth of focus. On the other hand, all objectives that are without that quality do not have the maximum defining power.*

The Genus Ligula.-M. Donnadieu holds that all the species described by authors as forming this genus are only the different phases of development of the same species, or the same parasite found in different animals, the so-called genus being simply a species of the genus Dibothrium-the Dibothrium ligula.

Nutriment of Bacteria.-MM. Dupont and Hoogewerff, of Rotterdam, have investigated the chemical constitution of the materials that nourish bacteria. Test tubes, like those used by Cohn, were filled with 20 c.c.m. of the nutrient fluid, and two drops of bacterium fluid, made with decomposing beans or peas, were added; the tubes having been first deprived of any atmospheric dust by hot water. Care was taken that the distilled water employed contained no organisms. Following Mayer, they prepared a normal nutrient fluid with 1 per cent. acetate of ammonia, 0.5 per cent. phosphate of potash, 0.5 per cent. sulphate of magnesia, and 0.05 per cent. phosphate of lime. As Mayer stated, they found the most important ingredient to * Carl Reddots, in American Journal of Microscopy.'

be phosphate of potash, and that the magnesian sulphate might be omitted without hindering the bacterium development. The following carbon compounds were tried in lieu of acetate of ammonia in the nutritive fluid. One per cent. of carbonate of ammonia gave no development; 1 per cent. of urea and the same of ethyl-urea no development; 1 per cent. formiate of ammonia, no bacteria, but some mycelium; 1 per cent. formiate of potash and the same of ammonia, bacteria development; 1 per cent. oxalate of ammonia, no development; 1 per cent. neutral acetate of ammonia, development; 1 per cent. of the acid acetate, no development; 1 per cent. acetamid, development; the same with 1 per cent. of glycocoll; no development with 1 per cent. of sulphate of anilin. The authors were led to the conclusion that only those carbon compounds served as food for bacteria which contained “carbon atoms not united with two of their affinities to oxygen."

Bacteria as Parasites in Splenic Disease.-M. H. Toussaint has communicated fresh remarks on this subject to the French Academy, his object being to show that those who have attributed the disease to a virus, and not to the bacteria, are in error. Referring to a previous paper, he states that a rabbit dying after inoculation with blood containing the bacteria dies in consequence of the obliteration of the capillaries of essential organs, such as lungs and brain. Most of the flexuous capillaries of the economy are filled with bacteria at the moment of death. This effect is most readily observed in the choroid and retina of albino rabbits. He claims to have demonstrated that when fresh bacteria blood is received in tubes and preserved from contact with air and from putrefaction, it loses its contagious properties in six or eight days, or sooner if kept at a temperature of 38° to 40° C. A virus does not behave in this way. Such a method would be adopted to preserve it. Filtration of bacteria blood, fresh and defibrinized, through a filter composed of eight sheets of paper suffices to deprive it of its contagious elements. This filter allows the granulations, and even some white corpuscles to pass, but it retains all the bacteria. Such a filtration allows a considerable quantity of virus elements to pass, but completely deprives bacteria blood of its contagious properties. The time elapsing between bacterium inoculation and the death of an animal may be regulated by the quantity injected and the pretended incubation period suppressed. In one rabbit 1 cubic centimetres of the affected blood were injected, containing some 1500 millions of bacteria; in another 75 millions; and in a third 1500, the blood being diluted with water. The first died in seven hours, the second in twelve or thirteen, and the third in thirty-six hours. He describes many other experiments, all confirming the belief that the death is produced by the multiplication of the organisms and their obstructing the capillaries.†

* "Der Naturforscher," March 9, 1878, copied from 'Maandblad vor Natuurwetenshappen,' 6 Jrg., No. 1.

+ Comptes Rendus,' March 18, 1878.

BIBLIOGRAPHY.*

The fourth edition of Beale's 'Microscope in Medicine,' and the second edition of Martin's Manual of Microscopic Mounting,' have just been issued; also a work by Dr. Dudgeon, the Human Eye; its Optical Construction popularly explained.' In Paris has been published the first part of Professor Ranvier's 'Histology of the Nervous System,' and in Leipzig the fourth edition of Dr. Willkomm's 'Die Wunder des Mikroskopes oder die Welt im Kleinsten Raume.'

Van Heurck's' Microscope applied to Botany.'—A new edition of this work is announced to be in preparation, considerably enlarged, and with the addition of a third part dealing exclusively with diatoms. M. Van Heurck's collection of diatoms is (according to Dr. Pelletan) one of the most important now existing, containing not less than 10,000 specimens. It includes all the types of De Brébisson, and the original collections of Walker Arnott, Eulenstein, and Kützing, without reckoning the numerous series of W. Smith, Grünow, Hantzich, Rabenhorst, &c. The collection of Kützing, which belonged to Eulenstein, was divided into two parts, of which one was sold to the British Museum, and the other, which Eulenstein reserved for himself, now belongs to M. Van Heurck.

The first volume of 'Science Lectures at South Kensington' contains the lecture by Mr. H. C. Sorby, F.R.S. (ex-Pres. R.M.S.) on "Microscopes."

The QUARTERLY JOURNAL OF MICROSCOPICAL SCIENCE for January contains:

On the Hinged Teeth of the Common Pike. By Charles S. Tomes.

Note on the Movements of the Vibracula in Caberea Boryi, and on the Supposed Common Nervous System in the Polyzoa. By the Rev. Thomas Hincks, B.A., F.R.S.

The Development of the Cranial Nerves in the Chick. By A. Milnes Marshall, D.Sc., B.A., Fellow of St. John's College, Cambridge.

A Contribution to the History of the Embryonic Development of the Teleosteans. By Ed. Van Beneden.

On the Homologies of the Suspensor. By Sidney H. Vines, B.A., B.Sc., Fellow and Lecturer of Christ's College, Cambridge.

The Red Vascular Fluid of the Earthworm a Corpusculated Fluid. By E. Ray Lankester, M.A., F.R.S.

The Contractile Filaments of Amanita (Agaricus) muscaria and Dipsacus sylvestris. By Francis Darwin, M.B.

On Atmospheric Bacteria. By G. T. Dowdeswell, B.A. Cantab.

A Review of Reichenbach's Researches on the Early Development of the Fresh-water Crayfish. By T. Jeffery Parker, Associate of the Royal School of Mines.

For April:

On the Phenomena accompanying the Maturation and Impregnation of the Ovum. By F. A. Balfour, M.A., Fellow of Trinity College, Cambridge. Notes on the Structure and Development of Osseous Tissue. (From the Physiological Laboratory of University College, London.) By E. A. Schäfer.

* See note on p. 79. The journals noticed will be found in the library.