salt mixture. The process was so tedious that a more expeditious method appeared desirable, and I therefore constructed an instrument for freezing with ether spray, and described it in the 'Journal of Anatomy and Physiology' for April, 1877. At this time I was informed that an instrument was described by Mr. Hughes in the same journal twelve months previously; but finding my microtome simpler in construction and more expeditious in freezing, I have employed it, with some slight modifications, up to the present time. The woodcut represents

in vertical section the freezing microtome which I constantly employ, and which I can very strongly recommend for general use. The lower half (a) is in principle an ordinary Stirling microtome; the upper half consists of a freezing chamber (b) and the section plate (c). As regards the microtome, I always insist upon the use of an oval instead of a circular plug (g), whilst the screw should be three-quarters of an inch in diameter, finely worked, and with a milled head at least of an inch wide. The freezing chamber (b) should have a false sloping bottom (f) leading to

b

с

a

h

an exit tube (e), which conducts off the condensed ether. Extremely simple as this contrivance appears, it is absolutely necessary for success that attention be paid to the following details of construction. The freezing chamber consists of a large hollow cylinder of zinc, slightly over two inches in diameter, and capped with a plate of the same metal. This cylindrical chamber is soldered on to the microtome plug, so as to ensure absolute steadiness in working, and it possesses three circular openings three-quarters of an inch in diameter, one placed in front of the two others laterally opposite each other. The section plate (c) is also made of zinc of an inch thick, and raised upon the vertical arm (d), also made of the same metal. The opening in the section plate should be sufficiently large to allow of the free play of the freezing chamber (b) through it without affording any point of contact between the two. With a freezing chamber such as the one described, beautifully large and thin sections may be obtained with ease. The material employed in the construction of the freezing chamber and section plate is a matter of importance, and I met with frequent failures and disappointments when endeavouring to utilize other more workable metals; brass above all metals was found unsuitable, and zinc alone fulfilled all the requisite conditions. Theoretically, it was supposed that the metal chamber should be covered with a non-conducting material, such as felt, wood, &c., and that the conduction between the section plate and body of the microtome should in like manner be cut off; but practically it was found that at the sacrifice of a small amount of ether rapid

freezing could be ensured and a large number of sections obtained before the tissues became loosened from the freezing chamber. It should be remembered, that to avoid the expense and incumbrance of a special condensing apparatus we have to provide for the free evaporation and subsequent condensation of ether in the same chamber, and consequently a sacrifice of about one-fourth the bulk of ether used is sustained. I regard as the requisite of a good freezing microtome the following conditions:

:

1. The instrument should be of the greatest possible simplicity. 2. The freezing should be rapid and expeditious.

3. The metallic constituents should be such as to retard thawing of the tissue when once frozen.

4. A minimum of ether should be expended.

Now, I would claim for my instrument a fulfilment of these conditions as far as is possible, without the employment of an exhausting and condensing apparatus; and I would on these grounds advocate its use by those who require a most satisfactory microtome, and one comparatively inexpensive. The first condition, that of simplicity, is too self-evident to dwell upon; the second also is ensured, as the tissue is frozen in less than twenty seconds, whilst it remains adherent to the cover of the freezing chamber for a period sufficing for the cutting of a dozen sections or more. A very small quantity of ether suffices for freezing, and three-fourths of its bulk becomes condensed, and may be collected in a bottle attached to the tube (e). I used a graduated bottle for the ether spray, and can thus read off the amount of ether expended in freezing. The costliness of ether has been urged against its employment in ordinary section cutting by one authority of note, and the objection would prove of great weight in case a large amount of ether was lost at each operation; it is but necessary, however, that the instrument be once seen in good working order to dispel all such notions from the mind, as the results obtained are of the first order, and the expenditure of ether very trivial."

The paper includes a description of the method of cutting sections of brain, but space prevents any further extract here, and the original may be profitably referred to.

Angular Aperture defined. Professor Romyn Hitchcock, of New York, brought this subject before the Indianapolis Congress. In order that the term "angular aperture" should mean something definite, and to avoid ambiguity and misunderstanding in future discussion on the subject, he proposed to adopt a definition of the term which, right or wrong, should be recommended to the microscopists of the country as a convenient and uniform usage. The triangle method was proposed for general adoption, considering the angular aperture of a microscope objective to be the angle of the apex of a triangle having a base equal to the available diameter of the front lens, and a height equal to the actual focal length (working distance) measured in air for a dry lens, and in the fluid employed for an immersion lens, the collar being adjusted for the most perfect definition in every case.

While nearly all the members seemed to be personally in favour

of the usage proposed, a motion that the Congress should attempt to settle the question by requesting its general adoption met with so much opposition that it was withdrawn.

Trichodonopsis paradoxa (Clap.).—The position, as regards classification, of this genus of Ciliate Infusoria, is said by the 'Micrographic Dictionary' to be doubtful. It resembles externally one of the Vorticellina, but is covered with well-developed cilia. The species T. paradoxa inhabits in myriads the intestines of Cyclostoma elegans.

M. A. Schneider contributes a note in regard to it to Comptes Rendus.' He says "it is common amongst the Cyclostomata of the neighbourhood of Poitiers. Its study has developed some interesting facts (complementary to those of Claparède and Stein), which I will briefly describe.

The cuticle presents over the whole of its surface, a very finely punctated appearance, resulting from the presence beneath it of an uninterrupted layer of little rods of circular section, disposed in 'palisades,' as may be seen in profile views. They are most easily observed on the basilar membrane of the disk. They resemble, in form and position, trichocysts, although without urticating filaments, and although they exist, as I have said, on the basilar membrane, which is constantly naked, without cilia or other appendages.

The problematical organ in the form of a solid cap, regarded by Claparède as muscular, and left undetermined by Stein, is the nucleus. It is hollowed out on one side; and in the notch, or opposite to it, is a small, very distinct spherical nucleolus.

This shows-1st, that the problematical organ and its satellite (nucleolus) are the only parts of the body which give with acids and colouring substances the characteristic reactions of the nuclear matter; 2nd, that several Trichodinæ, especially Neritilia fluviatilis, have a nucleus and a nucleolus, which correspond topographically to the organs which we consider as identical in the Trichodonopsis; 3rd, that the problematical organ, occasionally single, is sometimes double, triple, or quadruple; its division may indeed go farther, and it is not uncommon to find in the body six or seven tolerably large spherules, and from thirty to eighty smaller granules, representing altogether the nucleus of which they give the reactions; the nucleolus appears to remain undivided whilst the nucleus undergoes this fragmentation: it is thus shown that the problematical organ plays the same part here as the nucleus of the infusoria in reproduction by rejuvenescence; 4th, the impossibility of calling that a nucleus which Claparède and Stein have wished to consider as such in Trichodonopsis.

This organ, indeed, which surrounds the digestive apparatus, does not fix colouring reagents; its structure is special; its thickness is most commonly occupied by more or less bulky calculi; in fact, its very existence is not constant, for it is wanting in a whole category of individuals which are distinguished at the same time, by slight differences in the conformation of the superior extremity, and chiefly by an entirely different arrangement of the digestive apparatus; and this in such a degree that there is a real dimorphism in relation to the 2 c

VOL. I.

existence or absence of this organ, which can only be in my eyes a part fulfilling a very secondary glandular rôle.

The use of reagents has also enabled me to rectify several points relative to the structure of the disk and to the conformation of the digestive apparatus, of which I hope soon to publish the exact figures."

Importance of the Vegetable Cell-walls in the Phenomena of Nutrition. M. Max Cornu writes (in Comptes Rendus'):-"Sections of vegetable tissues sometimes extract the colour from solutions ; certain regions are brightly coloured, whilst others remain uncoloured. On immersing a transverse section of a monocotyledonous stem in a . weak solution of fuchsine, the sheaths of the fasciculi and the thickened walls colour brightly; in ammoniacal carmine, to all appearance of the same colour, the elements which are coloured are very different, being those which the sheath surrounds.

Colouring matters, with sufficient power, are thus divided into two groups; one being taken up by the thickened elements, the other not.

The thickened elements are the woody fibres and cells of dicotyledonous plants, hypodermic fibres, certain vessels, certain fibres of the liber, the sheath of monocotyledonous fasciculi, and generally the most external part of the cuticle; but these elements must be full grown.

The elements of the other group are young or thin, and generally covered with only a thin layer of protoplasm: these are the cells of the cambium, scalariform vessels, the collenchyma, &c. The ordinary cells, the vessels, and other elements may, according to the plants or the part of the tissue, be classed in one or the other category. The distinction of these two groups is easily obtained by means of sections of herbaceous stems of dicotyledons or of monocotyledons ; it is well to destroy the contents of the elements by acetic acid and to employ weak solutions.

The fixing of the colouring matters depends on the relative density of the wall; we get only an imperfect idea of this density from the colour and refraction. It is possible to follow by means of these reagents, the accumulation of new substance in the wall; the resorption of this wall in the spiral vessels of the fasciculi in process of elongation (Umbelliferæ, Cucurbitaceæ, &c.) is also easily observed.

The ordinary chemical reagents easily show that the colouring has no relation to the chemical composition; I have been able to study with this end, the pure products of M. Fremy (cutose, vasculose, cellulose), separated from the mass of complex substances. From a physical point of view these data were wanting.

We know the importance of the cell-wall in the interchange between the cells and the ascent of liquids; the experiments of M. Jamin have shown the value of certain physical forces, and notably of imbibition. But more than that, the walls may be the reservoirs in which are accumulated certain soluble principles drawn up by the

*Comptes Rendus,' vol. lxxxvii. p. 537.

root; it is thus easy to understand that the sap may be almost pure water, and that it could scarcely concentrate itself in the upper parts of the plant. subjected during summer to a considerable evaporation. The theory of the descending sap and the other theories left, in this respect, grave difficulties unsolved.

As to the substances which do not fix themselves on the walls of the elements, we imagine therefore that they must circulate in the plant in a very different manner. There is then a distinction to establish from a physical point of view, with reference to the cellwall, in the absorption and the migration of the substances dissolved. One of the groups of colouring substances contains (in the order of the colours of the spectrum):

Aniline black, hematoxyline, Coupier's blue, osmic acid, cyanide of iron, aniline blue, rosollic acid, ammoniacal carmine, juice of phytolacca, &c.

The other contains :

Methyl-violets and quinoline violet, diphenylamine blue, aniline green, Coupier's green, aniline yellow and brown, permanganate of potash, coralline, sulphocyanide of iron, fuchsine, rosonaphthaline, &c. These properties may be utilized, in approximate analyses, to eliminate easily certain substances sought for (in wines, syrups, &c.), or to concentrate them.

The sulphocyanide of iron acts upon the thickened elements (like the perchloride) and colours them the colour of dragon's blood; nevertheless a similar section rapidly loses colour in the cyanoferride of potassium, and precipitated cyanide of iron acts upon thin and plasmatic elements. It is seen that the secondary reactions may much modify the primitive distribution of the substances. In experiments on nutrition, reactions of this kind may give rise to errors.

The protoplasm and the nuclei of the elements when dead are rapidly coloured by the substances which act on the thick parts; but the whole easily loses colour. The substances of the other group colour more slowly, but in a more permanent manner, the nucleus especially. Experiments made in collaboration with M. Mer have enabled us to understand this fact.

The explanation of these phenomena of fixation are based on a physical action very similar to capillarity; the dimensions of the molecules and their interval ought probably to be considered: but this is not the place to dwell upon it.

To sum up, we see that physical forces may separate the matters absorbed by the plants from one another, according to a law easily demonstrated experimentally with coloured substances: very important consequences in regard to the phenomena of nutrition may be deduced therefrom."*

Mechanism for the Fertilization of Meyenia erecta.—Mr. R. Irwin Lynch, of Kew, describes, in the Journal of the Linnean Society,' a previously unobserved mechanism in this plant (an acanthaceous shrub of tropical Africa) for cross-fertilization. The anthers, which are *Comptes Rendus,' vol. lxxxvii. p. 303.