When mature of this form multiplies by fission for a period extending from two to eight days, it becomes peculiarly amaboid, two individuals coalesce, slowly increase in size, and become a tightly distended cyst. The cyst bursts, and incalculable hosts of immeasurably small sporules are poured out as if in a viscid fluid and densely packed; these are scattered, slowly enlarge, acquire flagella, become active, attain rapidly the parent form, and once more increase by fission. Experiments were next made to determine the influence of heat. An ordinary slide containing adult forms and sporules covered in the ordinary way was in seven several cases allowed to evaporate slowly and placed in a dry heat which was raised to 121°C (250°F). It was then slowly cooled, and distilled water was taken up by capillary attraction. On examination all the adult forms were absolutely destroyed, and no spore could be definitely identified. After being kept moist in the growing stage for some hours and watched with the 1-50th, gelatinous points were seen in two out of the seven cases, which were recognised as exactly like an early stage of the developing sporule, and by careful watching these were observed to attain the small flagellate state." The paper is a most valuable one, and well merits being read by those who have not yet done so.

A Mode of rubbing down Needles for Microscopical Work.—At a late meeting of the Reading Microscopical Society Dr. Shettle described a method of rubbing down needles so as to produce a cutting edge, and yet retain the sharp point, by running the needle edgeways through a slice of cork, allowing such portion only of the pointed edge to project as it is desirable to convert into the knife-blade. The cork, with the needle thus inserted, is then firmly fixed in a small hand-vice, the edge of the cork being brought to the edge of the vice. The needle should then be laid upon a block of metal or other hard material, and rubbed carefully with an oil-stone hone, the two sides of the needle-blade being easily produced by inclining the vice in a particular manner. The edge of the blade should always (for convenience of rubbing) be kept in one direction, and its place determined by keeping the needle much nearer one side of the vice than the other. The paper also referred to a form of handle, with tapering ferule, by which the knife-edged needle is very firmly fixed, and by the use of which a change of needle is easily effected.

Mr. Stephenson's Examination of Diatoms.-This method, which is described and illustrated very fully in the "Monthly Microscopical Journal" for July, is perhaps the most valuable novelty of the kind that has been yet recorded. Mr. Stephenson has conceived of the method of examining diatoms (and of course other objects) in solutions of different densities, and watching the result. The following paragraph from the paper will give a notion of the mode of working, but the original paper must be read by all who are interested in microscopy. Mr. Stephensons says: "If diatoms are examined in air, i.e. dry, they are, in some instances, too opaque for transmitted light, but on immersing them in water, of which the mean index is 1:336, they become more translucent; with media of higher refractive power the translucency increases until the mean index of strong sulphuric acid (1.434) is attained, in which they become practically invisible. As every object which is transparent and colourless becomes absolutely invisible when immersed in a colourless medium identical in refractive power with

itself, we know approximately that the refractive index of diatomaceous silex is 1-434 (much below that of quartz), and this is accordingly, for diatoms, our neutral point. Although I have said colourless objects mounted in a colourless medium become invisible, it is of course equally true if both are of the same colour and of the same index. By progressively increasing the refractive power of the mounting medium, the diatoms gradually again become more and more visible until, as we all know, when mounted in Canada balsam (1·540) the coarser species are sufficiently defined for all ordinary purposes; but if we require a still greater departure from the neutral point or invisible condition, we must select some other substance of still higher refractive power. This we find in bisulphide of carbon, the index of which is 1.678, being, I believe, the highest of any known fluid." The Mode in which Bacteria Multiply.-Herr Grimm, in the "Archiv für mikrosc. Anatomie," describes the reproduction of Bacteria and Vibriones from his own investigations. He has observed their conjugation and fissiparous multiplication, and also has seen leucocytes breaking up into granular matter, which ultimately assumed the form of Bacteria.

Irish Support to Microscopy.-The Royal Irish Academy has given the sum of 40l. to Mr. G. H. Kinahan, in order that he may continue his valuable researches into the microscopical structure of rocks, a subject on which for some time Mr. Kinahan has been engaged.

Mode of Observing Tissues in the Living State.-This subject, which is of the utmost importance at the present moment, was dilated on as follows by Mr. Schäfer, at one of the meetings of the Medical Microscopical Society. The report says that Mr. Schäfer, having dwelt briefly on the importance of the subject, remarked that the investigation of a subject was not complete till it had been microscopically studied in the living state, and that such examination, at least for warm-blooded animals, should be carried on at the temperature of the body. Much was to be learnt from the investigation of tissues still attached to the living body, for thus had cell migration been discovered by Cohnheim in the frog's mesentery, and experiments on embolism had been made in that animal's tongue; while the tail of the tadpole had taught us much about connective-tissue corpuscles, and the development of blood-vessels. Muscular tissue was best seen in the living state, in the smaller crustaceæ. Living tissues, removed from the body, allowed of being studied in many ways: some immediately without any addition whatever, as red blood corpuscles, and striated muscular fibre; while if any addition were necessary, a saline solution of 0.75 per cent., or serum would be best. For some purposes a moist chamber might be necessary, such as Recklinghausen's, in which frogs' blood had been preserved for days in a living condition (Schultze's "Arch." 1866). Another form was Stricker's putty stage, which was also useful for the application of electricity in microscopical research by means of two electrodes of tin-foil, the points of which nearly meet in the centre of the stage. Mr. Schäfer finally described and exhibited various forms of warm stages, one kind of which, as Schultze's, was heated by means of a lamp applied to metal arms, which conducted the heat to the object-bearers; another kind, as Stricker's, in which a constant temperature was maintained by means of a current of warm water kept continually flowing through it; while another very ingenious form of stage, somewhat similar to Stricker's,

was so arranged that a constant circulation of warm water was kept up in a closed system of tubes, the temperature of which was regulated by a mercurial gas-regulator, and measured by a thermometer, the bulb of which lay close to the central chamber.

How to make Atomic Lenses.-This very valuable prescription is given by Mr. F. Wenham, V.P., R.M.S., in the "Monthly Microscopical Journal " for July. His account is as follows: "Strips of clear thin window-glass were drawn out into threads with the blow-pipe flame; a portion was then held in the point of the flame and fused into a spherule of the desired size. A number of these may be formed in a short time. The spherical figure is pretty accurate up to one-twentieth of an inch in diameter. One precaution must be observed. The strips of glass from which the threads are drawn must be broken, and not cut off with a diamond; if so, the spherules will not retain a clear polished surface, as the rippled cut of the diamond leaves its mark to the last. The blow-pipe may be an ordinary portable one, and the flame of a common stearine candle gives heat enough. The glass used should be quite clean, and always be held as near the point of the flame as possible, in order to avoid the deposit of smoke. Large spherules so made take an elliptical figure. Should they be required above onetwentieth they are best formed thus:-Select a clean fragment of windowglass, broken off (not cut), of such a bulk as will form the desired sphere. Attach this by one corner, with heat, to the point of a platinum or iron wire. Now rotate the mass while in a state of semi-fusion by twirling the wire back and forwards between the finger and thumb, holding it sometimes up or down, horizontally or inclined, according to the way that the glass seems inclined to sink. With very little dexterity spheres up to one-fifth of an inch in diameter may be so obtained, the rotation of the wire enabling the figure to be appreciated with some accuracy. When cool the spheres are pulled off the wire, which enters but a little way. These spheres are useless things enough alone.”

The High-power Definition of Organic Particles.-On this subject a short but important paper appears in the "Monthly Microscopical Journal" for September. Dr. Pigott, F.R.S. (the author), endeavours to show that the markings on a Podura are purely spherical, just like those on Angulatum.

Progress of Microscopy in England during the last Three Months.-The following is a list of the titles of the several papers which have appeared in the "Monthly Microscopical Journal" for July, August, and September:Observations on the Optical Appearances presented by the Inner and Outer Layers of Coscinodiscus when examined in Bisulphide of Carbon and in Air. By J. W. Stephenson, F.R.A.S., Treasurer R.M.S., and Actuary to the Equitable Assurance Society.-Remarks on Aulacodiscus formosus, Omphalopelta versicolor, &c., with Description of a New Species of Navicula. By F. Kitton, Norwich.-Measurement of Immersed Apertures. By F. H. Wenham, Vice-President R.M.S.-On Bog Mosses. By R. Braithwaite, M.D., F.L.S.-On the High-Power Definition of Minute Organic Particles. By Dr. Royston-Pigott, M.A., F.R.S., F.C.P.S., F.R.A.S., M.R.I.-The Preparation of the Brain and Spinal Cord for Microscopical Examination. By H. S. Atkinson.— Researches on the Life History of a Cercomonad: a Lesson in Bio

genesis. By W. H. Dallinger, F.R.M.S., and J. Drysdale, M.D.-The Angular Aperture of Objectives. By Robert B. Tolles, U.S.A.— Remarks on the Confirmation given by Dr. Colonel Woodward to the "Colour Test." By Dr. Royston-Pigott, F.R.S., &c., &c.—Remarks on Mr. Carruthers' Views of Prototaxites. By J. W. Dawson, LL.D., F.R.S.-On Ancient Water-fleas of the Ostracodous and Phyllopodous Tribes (Bivalved Entomostraca). By Professor T. Rupert Jones, F.R.S., F.G.S.-The Pathological Relations of the Diphtheritic Membrane and the Croupous Cast. By Jabez Hogg, Surgeon to the Royal Westminster Ophthalmic Hospital, President of the Medical Microscopical Society of London, &c.-On Organic Bodies in Fire Opal. By Henry J. Slack, F.G.S., Sec. R.M.S.-On the High-Power Definition of Organic Particles. No. II. By G. W. Royston-Pigott, M.A., M.D., F.R.S., &c.-On the Apparent Relation of Nerve to Connective-tissue Corpuscles, &c., in the Frog-Tadpole's Tail. By R. L. Maddox, M.D., H.F.R.M.S.-On a New Sub-stage for the Microscope, and on certain Appliances for Illumination. By Edwin Smith, M.A.-The "Colour Test" and Dr. Pigott. By F. H. Wenham, Vice-President R.M.S.— Experiments on the Development of Bacteria in Organic Infusions. By C. C. Pode, M.B., Demonstrator to the Regius Professor of Medicine, and E. Ray Lankester, M.A., Fellow and Lecturer of Exeter College.

PHYSICS.

A Note on the Spectrum of Chlorophyll.-M. Chautard has a note on this subject in a late number of the "Comptes Rendus." After specifying the changes produced in chlorophyll by light, he makes reference to the persistence of green matter in certain plants late in the autumn season; he considers this due to the presence of fatty and resinous matters. He finds that a solution of chlorophyll in fixed oils (oil of belladonna, e.g.) is not sensibly altered after several days' exposure in full sunlight. The most luminous spectral rays are the most active in changing chlorophyll solution; and rays which have already traversed a layer of chlorophyll have no effect on a second layer so long as the first is not discoloured. In this experiment he used vessels with two or more compartments. Heat modifies chlorophyll, but does not readily destroy it at temperatures under 100°. Above 100° the chlorophyll undergoes various alterations, according to its degree of dryness and the nature of the solvent. Dried chlorophyll is completely disorganised at a temperature about 200°; whereas, solutions of it in essential oils only undergo a slow, gradual change at this temperature, and may even resist 225° or 250° for several hours.

Galvanic Reduction of Iron under the Influence of a powerful Electro-magnetic Solenoid.-M. Jacobi, of St. Petersburg, covered the interior walls of two glass vessels with cylinders of sheet-iron, and placed in these vessels two similar rods of wax, coated first with a thin electro deposit of copper, and then with plumbago. The vessels were then filled with a solution of sp. gr. 1.27, containing 135 parts of ferrous sulphate, and 123 parts of mag

nesium sulphate, rendered neutral by the addition of magnesium carbonate. One of these vessels was surrounded by a tube of sheet iron, in which was coiled a helix of insulated copper wire. A reducing current from one Smee cell was now passed through the solution in the two vessels, while another current from four Bunsen cells went through the magnetizing helix. At the end of twenty-eight days the wax rods were examined, with the following results: An equal weight of iron was deposited on each rod; but, while the iron on the rod not exposed to the heliacal current was smooth and fair, the iron on the other rod was principally on its upper and lower portions, in the form of tufts, having a crystalline structure, and resembling somewhat the appearance presented by a bar magnet after its introduction into iron filings. He found that both deposits were very feebly magnetic, and further experiments showed that iron deposited by electrolysis receives a remarkably high charge of temporary magnetism, and has very feeble coercive force; he therefore recommends such iron for the construction of electro-magnetic cores. Recent Estimate of the Velocity of Light.-M. Cornu has, we understand, repeated, with all the precautions suggested by the recent progress in physical science, the experiment of Fizeau to determine the velocity of light. His researches, which have extended over a period of three years, lead him to conclude that the toothed wheel used in this method is capable of giving more accurate results than the revolving mirror employed by Foucault. The principal station, containing the toothed wheel and the mechanism for rotating it, the means of illumination, the telescope, the velocity-register, &c., was at the École Polytechnique. The other station, in which the collimating telescope and the reflector were placed, was at Mont Valerien. The distance between them was carefully measured and found to be 10,310 mètres, with a probable error of less than ten mètres. The wheel was carried upon the arbor of the minute-hand of an improved clock-work. Three of these wheels were made use of, having respectively 104, 116, and 140 teeth. To the clock-work an electric apparatus to register the velocity of rotation was attached, and also the means for regulating its motion, and even reversing its direction. A velocity of 700 to 800 revolutions per second could be thus obtained, which was uniform, and perfectly under control. The registering apparatus consisted of a chronograph, upon the revolving cylinder of which three electro-magnetic pens made their marks; one of these marked seconds, the second marked the rotations of the toothed wheel, and the third, controlled by a key in the hands of the observer, marked the instants of eclipse. The calcium-light was generally employed as the source of illumination, though a simple petroleum lamp was also occasionally used. Over a thousand separate observations were made and registered upon the chronograph; but only the best of these, six hundred and fifty in number, were reduced. These reductions gave the following values in kilomètres, for the velocity of light as deduced from the various orders of the occultation:

The numbers in parenthesis express the relative value of the corresponding