NOTES AND MEMORANDA.

Trembley's Experiments on Turning a Hydra Inside Out.-Professor Th. W. Engelmann, of Utrecht, communicates the following to the 'Zoologischer Anzeiger' :-Among Trembley's many remarkable statements concerning the vital properties of Hydra none has awakened more surprise than that the animal after being turned inside out continues to live, and is able to take nourishment, to digest, &c. Whilst the statement, if it be correct, would involve the upsetting of many of the most important and apparently best founded morphological and physiological doctrines, yet, on the other hand, Trembley is noted as a most exact and credible observer, and it therefore seemed to me well worth while to repeat his experiments even at the risk of succeeding no better than honest Rösel, the only one I know of who appears to have repeated them carefully.

I have therefore every year since 1873 tried Trembley's experiment, in doing which I narrowly followed his directions. An animal of suitable size and a hog's bristle of proper size and shape, with a pretty steady hand, are all that is wanted. The experiment is by no means difficult. The results, however, were without exception unfavourable to Trembley's assertion.

The turned body of the polyp when it did not soon resume its normal position always perished within a short time, the cells, and first of all those of the entoderm, swelled very much, gradually loosened themselves from their connection, and were found after a day or two like a small white cloud at the bottom of the glass beneath or beside the remainder of the polyp, only the anterior part of the body containing the thread cells, and which consequently cannot be quite turned, remained alive in many cases, and (after the turned part had died and been pushed off) developed a new body from behind, sometimes in a slanting direction. Under the microscope this showed the ectoderm outside, and inside the entoderm, with their known histological structure. In many cases the whole polyp died.

That the conditions were not unfavourable for the success of the experiment, was evident from the fact that under precisely similar circumstances extremely small pieces of the tentacles cut off were frequently observed to develop into perfect five-armed Polypi, and Hydræ, which had been slit longitudinally, to grow together, &c.

For my first experiment I had taken animals from slow-running water. As Trembley's polypi were mostly derived from stagnant waters, I experimented afterwards with such specimens, but with the same negative results. There can therefore be no other conclusion come to than that this otherwise so careful observer has for once been deceived. Certainly if we re-peruse many of his minute descriptions we should like to think that we had done him injustice in this assumption, otherwise we are driven to the further conclusion that he sometimes describes things most minutely of which in reality he has seen the least.*

VOL. I.

*Zoologischer Anzeiger,' vol. i. p. 77.

T

On the Gold Method, and the Termination of the Nerves in the Unstriated Muscles.-Professor Ranvier contributes the following to the French Academy:-Among the methods employed in histology for studying the final ramifications of the nerves, the gold method is the best. It does not, however, give constant results. The old methods of Cohnheim, Gerlach, and Hénocque give clear and demonstrative preparations only by chance. The modification recently introduced by Löwit constitutes a real progress, for by following the procedure of this histologist we succeed much more frequently than by the old process in colouring the nerve fibrillæ, whilst the elements which surround them remain uncoloured or scarcely coloured. There is, however, a grave objection to this process-the solution of formic acid in which the fragment of tissue is placed before submitting it to the action of the chloride of gold, notably alters its delicate parts.

I have therefore sought other methods, and after many fruitless attempts, I have found the following, which nearly always succeeds, at least for some organs:-A cornea, which is an excellent subject for the gold method, is taken from an animal (either a mammal, a batrachian, or a bird) just killed. It is placed for five minutes in fresh lemon juice, filtered; then it is put for fifteen to twenty minutes in three cubic centimetres of a 1 per cent. solution of chloride of gold, then in twenty-five to thirty grammes of distilled water, to which is added one or two drops of ordinary acetic acid. Two or three days afterwards, when under the influence of sunlight and the slightly acid medium the reduction of the gold has been effected in the cornea, preparations are easily obtained, in which the nervous fibrillæ of the connective layer and of the anterior epithelium are excellently shown.

Fragments of striated muscles have been treated in the same manner, or better, after having been subjected to the action of the gold, they have been placed for twelve hours, sheltered from the light, in a solution of formic acid of 20 per cent., and then prepared by teasing. The muscles of the lizards (Lacerta viridis and L. muralis) have given me terminal nervous arborisations, such as I have never obtained by the process of Löwit. These arborisations, coloured a deep violet, are admirably clear, and show themselves under forms absolutely comparable to those which I have obtained by proof alcohol.

I now come to the important part of this communication, which relates to the termination of the nerves in the unstriated muscles. Histologists are not in accord as to the mode in which the nerves terminate in this kind of muscles. Some, as Trinchese, Frankenhauser, Krause, and Hénocque, while differing on points of detail, maintain that the nerve-fibres terminate upon or in the muscular elements by free extremities; the others, Klebs, J. Arnold, Löwit, and Gschleidlen, admit that the final fibrillæ resulting from the division of the motor nerve constitute a network, but they do not agree on the form, the position, and the extent of this network.

By means of the process above described, I believe I have succeeded

in determining the mode of nerve termination in the unstriated muscles. In the voluntary unstriated muscles of the gasteropod mollusca (Helix pomatia), the motor nerves are divided and subdivided apparently into fibrillæ, which are lost at the surface of the muscular cells by expanding and forming a terminal arborisation, diminutive and badly defined, to which may be given the name of motor plate (tache motrice). In the unstriated and voluntary muscles of the gasteropods there are no anastomoses between the motor nervous fibrilla; and henceforth a terminal nervous network cannot be admitted in their case. Amongst the mammals, batrachians, reptiles, and annelids, on the contrary, have been observed, in the organic unstriated muscles, a very complex nervous network, but branches of this network disengage themselves from the fibrillæ, mostly very short, which are lost at the surface of the muscular cells, there expanding, and forming an arborisation less clearly defined and still smaller than in the muscles of the gasteropods. From this somewhat summary explanation-sufficient, however, for what I wish to present to-day-it results that (1) In the unstriated muscles the nerves terminate, as in the striated muscles, at the surface of the muscular elements by an expansion, more or less arborised, of the cylinder-axis. (2) The nervous network of the involuntary unstriated muscles is in connection, not with the elementary nervous action which sets the muscle in activity, but with a more complex action on which depends the functional energy of an organ whose activity is derived from the direct action of the nervous centres. In support of this point I may refer to the fact that the muscular coat of the oesophagus of the mammals, which is formed in great part of striated bundles, but which does not contract under the direct influence of the will of the animal, possesses a plexiform nervous apparatus, and that an apparatus of the same kind appears on the striated musculature of the digestive tube of the anthropods.

It is scarcely necessary now to point out why the different authors who have studied the termination of the nerves in the unstriated muscles, in the different organs and in the different animals, have debated whether the termination is by free extremities or by networks. These networks exist, but in reality they constitute simple plexuses, from which the terminal fibrillæ disengage themselves.

Cover Adjustment for Microscope Objectives. The present mode of correction adjustment fulfils its purpose only within narrow limits, and beyond these, various secondary faults appear which seriously deteriorate the performance of even otherwise most excellent objectives.

The cause of this imperfection lies in the circumstance that the change in relative distance of the lenses composing the objective, by which the adjustment for cover thickness is at present sought to be effected, affects principally the chromatic aberrations, while the optical influence of the covering glass preponderatingly disturbs the correction of the spherical aberration. For instance, if both aberrations of an objective are corrected in the best manner for such rays as are reflected from an uncovered object, these rays will, as soon as the object is placed under a cover-glass, suffer from a spherical over

correction corresponding to the thickness of the covering glass, while the chromatic aberration is scarcely affected by it. In the adjustment for cover thickness at present, however, the relations of the aberrations are exactly the reverse, for by moving the front lens away from the other lenses of the system, the object-glass will become more chromatically than spherically corrected. An object-glass, therefore, which has been properly corrected for medium cover thickness, for instance, can by means of this adjustment be adjusted so far only as to correct either the spherical aberration absolutely and leave the chromatic aberration under-corrected, or in the most favourable case, under-correct the chromatic aberration, and over-correct the spherical aberration in such a way as to leave both remnants of equal value. Besides this, the distortions spherical as well as chromatic are only at a minimum when the lenses are at a certain relative position to each other; and as in objectives of high angular aperture these defects can anyhow not be quite removed, the extreme position will so increase them as to make not only the distortion and colour appearance at the margin of the field unpleasantly apparent, but to interfere seriously with the definition.

Furthermore, the changing of the relative distances of the lenses composing the object-glass seriously disturbs the focal relation of

these lenses, causing a change in the mag

nifying powers of the magnifying glass which interferes seriously with micrometric measurements.

To obviate all the above-mentioned difficulties, Mr. Gundlach has invented a new cover adjustment for object-glasses, in which he places before the front lens of the objective a transparent disk with parallel sides, capable of being moved by some mechanical means closer to or farther away from the front lens. The general mechanical construction or arrangement of the objective is shown in the accompanying woodcut from the Patent Office Report. In the space intervening between this disk and the front lens he places a transparent fluid of a refracting power equal to, or nearly equal to that of glass, affording thus, by increasing or diminishing the distance between the parallel disk in question and the front lens, and increasing or diminishing thereby the thickness of the layer of refracting fluid between them, a direct compensation for the increased or decreased glass cover of the object, and consequently of the aberrations, without disturbing the focal relations of the lenses of the object-glass, thus avoiding the increased distortions and the disturbance of the magnifying powers of the objective consequent upon and inseparable from the disturbance of the focal relations of the lenses composing the system of the object-glass.

The advantages of this arrangement are obvious, and summarized and recapitulated are as follows:-1. The adjustment exerts no deleterious influence on the corrections of the aberrations, and is equally as efficient for any thickness of the covering glass as for uncovered objects. 2. The working distance is the same for any cover thickness except for immersion objectives; for this reason objectives of very short working distance will with this adjustment admit of even the thickest covering glass. 3. The magnifying power is unchanged. 4. The image is placed but slightly out of focus. 5. The adjustment is very sensitive, thereby facilitating the exact rectification. 6. It can very easily be so arranged that the graduation on the adjustment rim shall indicate exactly the thickness of the cover. 7. Any casual and unavoidable defect in the movement of the adjustment has no influence on the centering of the objective, as any lateral displacement of the parallel disk causes no optical change whatever. The fluid between the front lens and the transparent parallel disk is glycerine, which has so far answered all expectation in a most satisfactory manner. Objectives made seven months ago have been sent long distances by rail without impairing their efficiency, and without loss or renewal of the glycerine. They might perhaps be used for years without the presence of any fluid being suspected. The new adjustment is applicable as well to immersion as to dry working objectives. It deserves to be mentioned, however, that for immersion objectives the advantages of equal working distances for every cover-glass thickness do not exist. It is, however, the reverse of what it is with the old adjustment, as the working distance will be the further the thicker the covering glass happens to be.*

The American Microscopical Congress. This Congress it is believed the first of its kind-met at Indianapolis, Ind., on the 14th-17th August last, under the presidency of Dr. R. H. Ward, of Troy. The following papers were read :

Aug. 14th.-"On the Limits of Accuracy in Measurement with the Microscope," by Prof. W. A. Rogers. Some New Forms of Mounting," by C. C. Merriman.

15th." On Mechanical Fingers," by C. M. Vorce. "On Angular Aperture of Microscope Objectives," by Dr. Geo. E. Blackham. "On the Definition of the term Angular Aperture," by Prof. R. Hitchcock. "On the Preparation of Ashes of Leaves for the Study of Structure," by Dr. R. H. Ward. "On the Classification of Algæ," by Rev. A. B. Hervey.

16th." On the Emigration of Blood-corpuscles in Passive Hyperæmia," by Dr. W. T. Belfield. "On a Standard Micrometer," by Prof. R. Hitchcock. "On a handy Rule for Micrometry," by C. M. Vorce. "On the Sting of the Honey Bee," by J. D. Hyatt.

"On

17th." On a New Section Cutter," by Dr. Carl Seiler. Biscol's Section Cutter," by Dr. R. H. Ward. "On the Progress of Microscopic Ruling," by Prof. J. Edwards Smith. "On the Construc

* American Journal of Microscopy, vol. iii. 135.