The eggs of the large infusoria are rare. Rain-water introduced with the greatest precautions into flasks (having their necks drawn out and sealed) rarely encloses rotifers, cyclops, keronæ, loxodes, &c., but bacteria are always found, very often monads, and sometimes rhizopods. On the other hand, 40 cubic metres of the dust, immersed in water freed from all germs, habitually give many species of large infusoria, although it may be difficult to recognize at once their eggs amongst the millions of germs in which they are distributed. 20 The cellules which are most diffused in the air are undoubtedly the spores of the Mucedina and of numerous cryptogamic productions, whose diameter varies from 10 to 100 of a millimetre. Then come the fructifications of certain fungi whose dimensions, more considerable, sometimes reach of a millimetre. I refer to those septate bodies or germinative masses swollen up in the form of spindles, gourds, or clubs. Then come pollens of very variable size and colour, then grains of starch, which are to the other matters as 1 to 100 or thereabout, and lastly the green alga which the air transports sometimes in voluminous quantities. The author concludes by pointing out that it would perhaps be useful and interesting, as bearing on questions of public hygiene, to extend to the corpuscles of the vibrions this kind of statistical study.* The Foraminifera and Polycystina of the North Polar Expedition of 1875-76.-Mr. H. B. Brady, F.R.S., describes in the Annals and Mag. of Nat. Hist.' for June, the results of his examination of the soundings from depths of 10 to 220 fathoms brought home by the expedition. After stating that the area represented by the collection is altogether new, the author says that there are about half-a-dozen species of Foraminifera that may be regarded as essential constituents of the microzoic fauna of these high latitudes, having been found at almost every depth at which the floor of the sea has been examined. They are, Globigerina bulloides (a dwarf variety), Cassidulina laevigata and C. crassa, Truncatulina lobatula, Pulvinulina Karsteni, and Polystomella striatopunctata, usually accompanied by one or two forms of Nonionina, varying according to depth and other circumstances, and, if the sea-bottom be composed of rough sand or gravel, by Polystomella arctica. Other species occur in every sample of mud or sand, wherever obtained; but it is not too much to say that those above enumerated constitute ninety-five per cent. of the entire collection made from these soundings. The constant occurrence of Cassidulina lævigata, of full size and well grown, even when the other Foraminifera accompanying it were poor, starved specimens, and the presence of Pulvinulina Karsteni in almost every dredging, to the practical exclusion of all other species of the same genus, are points of considerable significance. The almost complete absence of the Milioline genera (for the occurrence of a single, minute, thinshelled specimen here and there in a few of the soundings amounts to absence in such a case) is an unexpected feature. In dredgings at similar depths but little to the south of those under consideration 6 the simple porcellanous forms are comparatively common; and their area of distribution is otherwise world-wide; yet it is hardly too much to say that no approach to a full-sized mature specimen of any of the modifications of the Milioline type has been met with in the North Polar material. One or two of the species are undescribed hitherto; and a few others present characters somewhat modified by their boreal habitat. Here and there in the finer portions of some of the soundings, the siliceous tests of Radiolaria were observed; but at one station only, and that the most northerly of all, were they met with in any abundance. Professor Haeckel, to whom the mounts were submitted, considered that the species are, as far as they go, exactly identical with those found in the Challenger' soundings from the sea-bottom in the middle of the Pacific, from about 8° N. to 8° S. of the equator, at depths of 2400 to 2900 fathoms. He also confirmed the view which Mr. Brady had already arrived at, that, until we have the wider basis for accurate nomenclature which the publication of the 'Challenger' Radiolaria will afford, it is better to give nothing more than an enumeration of the genera observed. In summing up the general results the author points out that, with respect to the Foraminifera, we are now able to add to the previous researches (which have rendered account of the Arctic fauna as far north as lat. 76° 30′—that is, to within 13° 30′ of the North Pole)-three further instalments, namely, the group of soundings in Smith Sound and the north of Baffin's Bay, a single one in Hall Basin, and a series to the north of Robeson's Channel. These extend our knowledge of the sea-bottom to lat. 83° 19' N., a distance of 6° 49', more than half the interval between the most northerly point of previous researches and the actual North Pole. From a zoological point of view the result is not less gratifying. Sir E. Parry's soundings in Baffin's Bay, which, taken together, furnish the northernmost section of Messrs. Parker and Jones's table, yielded seventeen species of Foraminifera. All but three of these have been found in the soundings; but they form only a small part of the catalogue of fifty-three species which appear in the table accompanying the article. Setting aside the Norwegian lists given by the same authors, as representing a fauna more or less influenced by the warm current of the Gulf Stream, the Hundee Island and Baffin's Bay columns give an aggregate of fifty-five species, or only two in excess of the total now recorded. The facts which have been elicited, therefore, appear to indicate that there is no very striking diminution in the number and variety of the Rhizopoda as we approach the North Pole. Thirteen species are figured on two plates. On Examining, Preserving, and Photographing Bacteria.--Dr. Koch, of Posen, has published an interesting article in Cohn's 'Beiträgen zur Biologie der Pflanzen,' Bd. ii. Heft 3, of which the following are the chief results: For a long time attempts have been made to improve the method of examining Bacteria, such as the hæmatoxyline staining of Weigert; the process for the cultivation of Bacteria in long glass tubes introduced by Salomonsen, which rendered their thorough isolation in putrifying blood possible; also the experiments of Frisch on the spread of putrifying organisms in tissues and the inflammatory appearances caused by inoculation of the cornea. The principal difficulties which arise in investigating Bacteria are, as Dr. Koch considers, connected with their small size, their movement, the simplicity of their form, and their want of colour or power of strongly refracting light. But an equally great hindrance has been the want hitherto of a process for preserving the Bacteria in their natural shape and position, and producing undistorted representations of them. To obviate these difficulties the author adopted a process which consists in drying on the covering glass a very thin film of the fluid containing the Bacteria, in order to fix the latter in a plane. This film is afterwards treated with staining fluids and again moistened, so as to bring back the Bacteria to their natural forms and make them more plainly visible. The preparation is then enclosed in a preserving fluid, and finally photographed, to produce representations true to nature. The separate parts of this process are conducted as follows:First, the drying. A drop of the fluid containing the Bacteria is spread out in as thin a film as possible on a covering glass, so that Bacteria, blood-corpuscles, &c., do not overlap, but are separated by a space more or less great. Generally the preparation is ready after a minute or two for further manipulation. Albuminous fluids, and especially blood, are left somewhat longer to dry-if possible, a few hours. Covering glasses thus prepared may lie for months, and the dried Bacteria will be unchanged; they must, of course, be carefully protected from dust. The objection which might be raised against drying them thus, viz. that their form must thereby be considerably altered is, as experience has taught the author, unfounded; for he observed, to his astonishment, that the Bacteria did not shrink together into shapeless masses; but, like rigid bodies surrounded by a slimy sheath, adhered to the glass by this sheath, and dried without visibly altering their shape, particularly as to length and breadth. The second part of the process consists in moistening and staining the dried film. For the moistening a solution of acetate of potash (one part in two parts of distilled water) may be used with good results; a swelling without separation from the glass being brought about, and at the same time the Bacteria resume perfectly their original form, only appearing rather paler and more transparent than before. Since the Bacteria which have swelled up again in this fluid do not change any further, it is specially adapted to preserve the preparation, which may be forthwith cemented. The Bacteria are often too pale for examining and photographing, and must be made more distinct by being stained. For this purpose the aniline colouring matters appear to the author to be the most suitable. The Bacteria take, in fact, the aniline stain so quickly and completely that these colours may be used as reagents, to distinguish Bacteria from crystalline and amorphous precipitates, as also from the finest fat-globules and other minute bodies. Moreover, the aniline dyes, in their solution in water, act like the acetate of potash, as they soften the film but do not loosen it from the glass. Amongst the aniline colours, methyl-violet and fuchsin appear to the author to work best; he especially recommends the methyl-violet which is marked B B BBB in the price lists. When it is wanted to make the object more conspicuous for photographic plates aniline brown should be used. For preserving the preparations thus stained, either Canada balsam, a concentrated solution of potash, or glycerine may be used. Those preparations only which have been coloured in methyl-violet or fuchsin are adapted for placing in balsam. After being taken out of the staining liquid they are thoroughly dried and laid in the balsam in the usual way. Preparations coloured with methyl-violet and fuchsin, when they are to be photographed, must, in order to preserve the Bacteria in the most natural form, be placed, whilst still moist, in the solution of acetate of potash, and that must be done directly after they are taken out of the staining solution, and they should then be sealed. Glycerine, as it takes out the colours, will not do to place these preparations in; on the other hand, it is the best preserving fluid for preparations coloured with aniline brown. As regards photographing, the Bacteria are not different from other microscopic objects. As, according to the process above described, the film to be photographed is immediately under the covering glass, the employment of the strongest immersion objectives is possible. Under favourable conditions living Bacteria, which are not in a state of motion, may even be photographed, of which the author gives an example in a "photogram." He draws attention to the fact, that the photographic plate reproduces the microscopic image generally better, that is more surely, than the impression on the retina of the eye can be. The article itself gives very explicit details of the process in photographing. As proof of the excellency of the productions obtained by his process the author gives three plates, containing twenty-four specially fine photograms"; on which the most delicate details, as, for instance, the flagella of the Bacteria, are plainly visible.* 66 A Moist Chamber of very simple construction for observing the copulation of the Spirogyra is described by Dr. Strassburger, in his book on 'Fertilization and Cell Division.' It consists of a ring of cardboard soaked in water, on which the covering glass is placed. The drop of water containing the Spirogyra must be suspended from the under surface of the covering glass, and may then be preserved for several days, and the copulation readily observed. If the plants are placed under the covering glass in the usual way, they will infallibly die. The "Zentmayer" New Patent Microscope.-This instrument, which has just been introduced into this country by Messrs. Ross, resembles in appearance the well-known Jackson form of stand, but differs from it in the following particulars : : The limb supporting the body with the slide for quick adjustment, carries also a second slide, parallel with, and at the back of the other, by means of which a slow adjustment is obtained by the action of a stout steel lever passing through a channel in the limb; the lever is acted upon by the ordinary micrometer screw in conjunction with a stiff steel spring. This arrangement permits of the milled head of the fine adjustment being placed in a most accessible position, on a step above the trunnions supporting the limb and body of the microscope, almost similar to the fine adjustment in the old Ross model. This simple fine adjustment, when in use, leaves the body of the instrument quite untouched, and therefore not liable to swerve; an evil of common occurrence in cases where the fine adjustment is attached to the body itself. The magnification of objects is not altered by a difference in the length of body, as is more or less the case when the fine adjustment is obtained by means of a cylinder sliding in the nozzle of the instrument, and the thickness of an uncovered object on the stage can be directly measured by means of a divided scale and vernier which can be attached to the limb at the edge of the fine focussing slide. The most important feature of the Zentmayer stand consists in an improved method by which the tail-piece or stem carrying the mirror, sub-stage, with all illuminating apparatus, can be turned aside or swung on a tubular pivot (placed at the back of the stage), the centre of which is in a line in the optic axis intersecting the plane of the object on the stage, and consequently also in the focus of the object-glass. The use of this swinging tail-piece arrangement enables condensing and other lenses for concentrating light to be used at any angle below or even above the stage if required, affording peculiar facilities for obtaining oblique illumination, and in the adaptation of appliances to be used for the purpose. For registering the angle at which an object is best observed there is a divided arc on the upper segment of the swinging stem. With the usual form of microscope stand, in which a fixed stem supports the sub-stage, oblique light has to be obtained either by the use of separate reflecting prisms or admitting light through peripheral stops from the margin only of high-angled condensers. These necessarily come very close to the slide, and there is a difficulty in regulating the obliquity of deficient marginal rays. In the Zentmayer stand, however, with the use of the swinging arrangement, condensers and illuminators of long focus can be used with great advantage, and abundance of light is obtained with low-power objectglasses such as the 1 inch and 1 inch. In order to get the best results for oblique illumination a very thin stage was found to be requisite; a simple mechanical stage, with concentric rotary movement, has therefore been designed specially for this instrument by Mr. Wenham, having only one movable plate in its construction, the rectangular directions of which are performed by two concentric milled heads, something similar to the well-known Turrel stage. This stage is supported by a conical stem, which passes through the tubular pivot of the swinging tail-piece |