consist apparently of "illusory beads," and the belief now appears to be, with the most unbiassed observers, that they are such.

The Degeeria domestica, or speckled Podura, when shown opaquely* under a th or upwards, is a specially beautiful object. The scales are apparently much thicker than in other species, and the ribbings or !!! markings are of a reddish-brown colour-not beaded, but slightly constricted at regular intervals, like the short antennæ of some insects, and in the deep intercostal spaces there are numerous thin septæ, or transverse bars, very fine and distinct, of a greyish tint. Both these and the slightly "varicose" spaces on the ribs may be displayed in the form of beads, by dodging the illumination. Where practicable, some form of opaque illumination should always be employed for verifying the structure of these objects, for we are in this case quite free from the errors of diffraction, which more or less accompany objects seen by transmitted light, and cause an indistinctness of outline.

*The only plan at present known to me of illuminating these and other dry test-objects is the one that I recently described, and consists in mounting them, not on the cover, but on the slide itself. When the light is totally reflected from the upper surface of this at the part where the object is in contact, total reflexion will not occur, but the light will pass into the object, and in many casesas with some diatoms and the Podura-illuminate it with sufficient brilliancy on a black field to be plainly seen with the highest powers and eye-pieces.

There are several methods of securing this total reflexion, some of which are described in my paper "On a Method of Illuminating Opaque Objects under the Highest Powers of the Microscope," read before the Microscopical Society on March 26th, 1856, and published in the Transactions.' One of them consists of a solid glass parabola with a flat top, upon which the slides were placed, with an intervening film of highly refractive medium; this was made at the time, and ever since has been in use, mostly for viewing aquatic animalcules and living diatoms, &c., for which it is especially convenient. The parabola is first lowered so as to bring its top below the level of the brass table, and the object in a drop of water is covered with thin glass. The parabola is then screwed up till the object is secured. The rotifers are beautifully shown this way; but I have found that for objects on slides its use is not so convenient as the small truncated or nearly hemispherical lens and the ordinary parabola, as this arrangement affords greater facility for traversing the object, as there is sufficient play for the lens for this purpose in the hollow top.

As some have complained of a difficulty in using this, I repeat the directions. The little lens is first patched on under the slide with a minute drop of oil of cloves or turpentine where the Podura scales or other objects lay thickest. The slide is then put on the stage with the lens in the top of the parabola. The next thing is particularly to obtain parallel light. A large bull's-eye condenser should be employed with its flat side towards the lamp: hold a sheet of paper over the plane mirror, and see that the light falls in the centre, and is of the same area as the bull's-eye or about fills the mirror; then go through the ordinary adjustments, and if the field is not quite black raise the stop of the parabola: look at the objects with a low power, those only that are brilliantly luminous are on the slide. Select a proper one, and if it does not appear nearly in the centre of under lens, shift this beneath it. One cause of failure may be the absence of objects detached from the cover on the slide; but in English mounted objects, either of diatoms or scales, I have in most cases found a few straggling specimens that have left the cover. Possibly the figure of some of the paraboloids may have degenerated since I supplied the original steel template near twenty years ago, which must have been worn out before now; but this I will see to.

III.-On some New Parasites. By T. GRAHAM PONTON, F.Z.S., Honorary Secretary Bristol Microscopical Society.

PLATE XCI.

SOME time ago I described a new parasite from the tiger, in the pages of this Journal. I now propose to present to its readers four parasites, which I believe to be hitherto undescribed, or new.

Menopon ptilorhynchi (mihi) (Plate XCI., Fig. 1).—Colour bright fulvous. Head obtusely subtriangular; clypeus rotundate, vertex rounded, base concave. Two broad irregular chestnut markings extend from the insertion of the antenna to the eyes, which are connected at that point by a semilunar chestnut line, a chestnut spot in the centre of the clypeus; prothorax elliptical; metathorax transverse; abdomen ovate, hairy; all the segments, except the last, have a chestnut spot; legs long, tarsi clavate. Length 2.115 mil. Habitat, Ptilorhynchus holosericeus.

Nirmus Nitzschii (mihi) (Plate XCI., Fig. 2).—This species is probably the same as that mentioned in Griebel's list of the Halle Collection, without either name or description. Supposing this to be so, and that it is undescribed and unnamed, I have ventured to call it Nitzschii, after the indefatigable student of these peculiar insects, C. L. Nitzsch, and beg to give the following description of it :-Colour pale yellowish-white. Head panduriform, clypeus rounded, antennæ rather long, second joint longest. Prothorax not so wide as the head; metathorax oblong, trapeziform. Abdomen lanceolate, a long fascicule of hair between each of the four last segments. Legs somewhat clavate. Length 2-538 mil. Habitat, Ptilorhynchus holosericeus.

Docophorus Dennyii (mih) (Plate XCI., Fig. 3). This species I have dedicated to the late Mr. Denny, of Leeds, to whom I am indebted for much kind advice and assistance in the study of the Anopleura. Colour tawny. Head triangular, clypeus produced entire; trabeculæ large, broadly truncated; antennæ rather long. Clypeus bordered by a chestnut line, with a transverse semilunar marking of the same colour, a similar one on the occiput; a broad irregular chestnut mark extends from the eyes to the prothorax. Prothorax transverse, angles rounded, metathorax transverse. Abdomen ovate, hairy; pale fulvous, with a chestnut border. Length, 3.173 mil. Habitat, Prismites Mexicanus.

Trichodectes leporis (mihi) (Plate XCI., Fig. 4).—Colour bright fulvous yellow, a dark chestnut spot at the eyes connected by a diagonal line with a line of the same colour on the occiput. Head suborbicular; clypeus rounded, vertex convex, lateral margin deeply sinuated; eyes prominent; antennæ small, last joint broadly clavate; prothorax transverse; metathorax not so wide as the head. Abdomen ovate, fulvous, hairy. Tibia clavate. Length, 2.538 mil. Habitat, Lepus cannabinus.

CLIFTON, May, 1871.

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IV.-On some Improvements in the Spectrum Method of Detecting Blood. By H. C. SORBY, F.R.S., &c.

In the following paper I shall give a condensed account of what I have been able to learn in connection with this subject, and omit everything that does not bear directly on determining whether any stain is, or is not, due to blood. There does not appear to be any probability of our being able to decide by this means whether it is, or is not, human.

The spectrum-microscope used in these inquiries should have a compound prism, with enough, but not too great, dispersive power, or else the bands would be as it were diluted, and made less distinct. A combination of two rectangular prisms of crown glass, with a rectangular of very dense flint, and another of less dense, of such an angle as to give direct vision, turned towards the slit, as lately made for me by Mr. Browning, appears to be the proper medium, and has other important advantages. The cells used for the experiments should be made from barometer tubing, and be about one-eighth of an inch in internal diameter, and half an inch long, one end being fastened to a piece of plate glass with purified gutta-percha, like an ordinary cell for mounting objects in liquids. It is, however, a very great advantage to insert between the plate and the cell a diaphragm of platinum foil, having a circular hole about two-thirds of the internal diameter of the tube, fixed so that its centre corresponds with that of the cell. This prevents any light passing upwards that has not penetrated through the whole length of the solution, which is very important when using direct concentrated sunlight to penetrate through turbid or very opaque liquids. A small spatula made of stout platinum wire, flattened at the end, is very convenient for adding small quantities of the reagents; and they should be stirred up in the cells with a platinum wire, flattened and turned up square at the end, like a small hoe. The reagents commonly employed are a somewhat diluted solution of ammonia, citric acid, the double tartrate of potash and soda, used to prevent the precipitation of oxide of iron, and the double sulphate of the protoxide of iron and ammonia, employed to deoxidize; but in some special cases diluted hydrochloric acid, carefully-purified boric acid, and sulphite of soda are required.

The character of a stain varies much with its age, and with the nature of the substance on which it occurs. If quite recent, and if the substance has no immediate influence on blood, the stain would contain little or no colouring matter but hæmoglobin. This is easily dissolved by water, and when properly diluted-neither too strong, nor too weak-it gives the well-known spectrum, with two dark absorption-bands in the green. The addition of a very little

ammonia and a small quantity of the double tartrate produces no change, but on adding a small piece of the ferrous salt, about th of an inch in diameter, and carefully stirring, so as to mix without much exposure to the air, these bands gradually fade, and are replaced by the single broad and fainter band of deoxidized hæmoglobin. When stirred up so as to expose well to the air, the two original bands of oxidized hæmoglobin can be seen again. On gradually adding a little citric acid, until the colour begins to change, these bands slowly fade away; and, if the amount of blood was considerable, a faint band would make its appearance in the red. When previously deoxidized, this solution may be turbid, but not so as to interfere with the result. The addition of excess of ammonia makes all clear again, but does not restore the original bands, or only to a slight degree, thus showing that a permanent change is produced by citric acid-the hæmoglobin is changed into hæmatin. This alone serves to distinguish blood from by far the greater number of coloured substances, which after being changed by acid, are restored by alkalis to the original state. On deoxidizing with the ferrous salt, we obtain the well-marked spectrum of deoxidized hæmatin, with one very dark and another much fainter band in the green, almost or quite invisible when the quantity is small. If too much citric acid or double tartrate had been added, this solution might be turbid; but, if all had been properly managed, it would be quite clear. Since the deoxidization takes place rather slowly, especially in cold weather, it is well to slightly stir up the ferrous salt at the bottom, completely fill up the cell, cover it with a piece of thin glass, remove the excess of liquid with blotting paper, and mix the solution by turning the tube upside down, over and over again. On reoxidizing the solution by stirring, the bands of deoxidized hæmatin disappear, and the two bands of hæmoglobin will probably be recognized, owing to citric acid not changing the original merely into hæmatin, but also giving rise to some methæmoglobin. The whole of these facts may be seen with a single cell, containing about th of a grain of blood, and any experimenter should become quite familiar with them before applying this method to suspected stains in cases of importance. Very faint bands are best seen by lamplight.

On exposure to the air in a damp place, a blood-stain may be completely decomposed by the growth of mould, but when not thus destroyed it is partly altered into hæmatin. If, however, kept dry, the hæmoglobin gradually changes into a variable mixture of methæmoglobin, hæmatin, and a brown substance not yet much studied. This change takes place far more rapidly in the acid atmosphere of towns and houses, especially when gas is burned, than in the open country; but it does occur even in the purest air, and in glass tubes hermetically sealed. The presence of a weak acid in perspiration may also cause a stain on a worn garment to be completely changed

in a very short time, and the presence of a stronger acid on dirty clothes may at once alter the hæmoglobin into hæmatin.

On digesting in water a stain that has been kept until all the hæmoglobin has disappeared, the methæmoglobin dissolves. When the solution is sufficiently strong, this shows a band in the red, and two fainter in the green. The addition of ammonia removes that in the red, makes those in the green much darker, and develops a special very narrow band in the orange. When deoxidized this solution gives deoxidized hæmoglobin. Since methæmoglobin is formed at once from hæmoglobin by the action of a great number of different oxidizing reagents, and since it can be reconverted into oxidized hæmoglobin by slight deoxidization, I am inclined to look upon it as a peculiar oxidized modification. On adding a little of the double tartrate and of the ferrous salt to even a dilute solution from an old stain, the methæmoglobin is deoxidized, and the well-marked spectrum of fresh blood can be seen. If left too long, the spectrum of deoxidized hæmoglobin is developed, but on well stirring, that of the oxidized reappears, and the various other spectra may afterwards be obtained, as described above. That part of the stain, insoluble in water, which is chiefly hæmatin, may be dissolved in dilute citric acid or ammonia, and when deoxidized the spectrum seen to even greater advantage than when fresh blood is employed, because there is no general shading in the green, due to there having been methæmoglobin mixed with the hæmatin. We may thus obtain an excellent spectrum from a blood-stain nearly fifty years old. In very old stains all the methæmoglobin has disappeared, and sometimes even a considerable part of the hæmatin has been altered into another brown colouring matter, which does not give any wellmarked spectrum.

When a blood-stain has been made sufficiently hot to coagulate the albumen, neither water, citric acid, nor cold ammonia will dissolve it, but by heating in dilute ammonia the hæmatin is easily dissolved, and may be detected either before or after concentrating the solution by evaporation. I may here say that the spectrum of deoxidized hæmatin can in no way be better seen than by deoxidizing a solution of fresh blood that has been boiled with dilute ammonia, which gives rise to a very pure hæmatin.

In applying these principles to the detection of suspected stains, it is desirable in the first place to examine a portion of the unstained fabric, to ascertain whether any colour is dissolved from it by water, and whether the solution has an acid, or alkaline, reaction. It is also important to ascertain whether colour is dissolved from the fabric by dilute citric acid or dilute ammonia, and if so, to determine whether this would in any way interfere with the recognition of blood by the processes described above. In the case of scarlet cloth and of some other red fabrics, much colour is dissolved out by