Central Filament Research Articles

The fine structure of the sea urchin spermatozoa as revealed by the electron microscope.

The ultrastructure of the sea urchin spermatozoon has been studied by means of electron microscopy in ultra-thin sections prepared according to the technique of Sjostrand. 1. A cellmembrane covers the spermatozoon completely; it is a double membrane with a total thickness of 100 A units. 2. In the acrosomal region there is a particle—diameter 0.24 μ—and under this a cave filled with a less osmiophilic substance. In some Strongylocentrotus spermatozoa there is a vacuole near the bottom of this cave, it is divided into two parts, its walls measure around 200 A, and its dimensions are about 0.1×0.2 μ. 3. The nucleus has a few small spaces with nucleoplasm within a rather homogeneous mass of irregular particles with a mean size of 95 A. The nuclear membrane is double and has a thickness of 140 A. 4. The middle piece is filled with mitochondrial double membranes of 190 A; these are parallel with each other, but otherwise with random orientation. No division of the middle piece to subunits has been found. 5. The centriole is at the anterior end of the tail, located in a depression of the posterior part of the nucleus; it appears as a curved disk with a diameter of 0.15 μ. 6. Eleven filaments start at the centriole, there are two central ones which appear as single circular tubuli, there are nine peripheral ones, which appear as doublets or even triplets, with each unit having a diameter smaller than that of the central filaments. All filaments follow a straight course, have no striations and are not surrounded by helicoidal sheats. These findings are discussed together with current theories regarding sperm tail and cilia movement. 7. The tail end consists of the cell membrane and often single filament units formed by the more proximal forking of some filament doublets.

Further studies of the mosaic fungus.

IN CLEARED preparations of skin taken from mycotic lesions, one often finds patches of refractile debris arranged in a network. This is the much-discussed "mosaic fungus." It is illustrated in a scale from a mycotic lesion on the palm of the hand (Fig. 2<i>A</i>). The filaments of the mosaic fungus may be from 4.5 to 12 μ in width. In small mosaic deposits, the central filaments are the widest while the peripheral ones are narrow and attenuated. The network is composed of linearly arranged segments, sometimes short and rectangular, sometimes long and sinuous. Some believe that the mosaic fungus is the result of fungus infection; others, that it has no connection with mycosis. A number of years ago, Dowding and Orr summarized conflicting views about it in the Archives.¹The present article is an account of observations carried out since that time. ITS NATURE—FIVE INTERPRETATIONS 1.<i>Cholesterol</i>.—When

The submicroscopic organization of vertebrate nerve fibres: An electron microscope study of myelinated and unmyelinated nerve fibres

1. I. Thin serial frozen sections of fresh peripheral and central myelinated nerve fibres from the frog, rat, cat and rabbit, in addition to spinal cord segments of frog and rat, were examined with the electron microscope after freezing-drying or fixation with osmium. Supplementary investigations included parallel observations by phase contrast microscopy and examination of thin sections of embedded nerve, replica-adhesion and dissociation preparations. 1. 1. The following structures are described in the internode portion of the peripheral myelinated nerves: 1.1. a) The myelin sheath of fresh nerve separates into layered membranes which closely resemble the myelin lamellae of fixed whole nerve. Lamellar membranes of this type with an average thickness of 80 Å and a granular fine structure have been found in all nerve types. By means of ultracentrifugation of fresh whole nerve these laminated membranes can be warped in a reproducible fashion, indicating that they are probably preformed structures in the sheath. Dissociation of the fresh, unfixed membranes into rod shaped granules 60–80 Å long is produced by trypsin digestion. The concentric laminated structure of the sheath, consisting of individual layers approximately 80 Å thick, could be confirmed in all nerve types examined. 1.2. b) Oblique clefts corresponding to the Schmidt-Lantermann incisures were observed in the myelin sheath, and further structural details of the neurilemma membrane, its associated fibre bundles and the Schwann cells noted. Numerous opaque, oval bodies (0.5–1 μ) with a granular internal structure were found close to the Schwann cell. 1.3. c) An arrangement is described for obtaining successive electron diffraction patterns and electron micrographs from restricted areas of the same object in the specimen holder of an RCA EMU electron microscope, without breaking the vacuum. With this arrangement, characteristic cross-grating and Kikuchi line patterns have been recorded from crystalline structures resembling myelin lamellae in osmium fixed preparations. The evidence available suggests that these crystalline lamellae are osmium products formed in the nerve during the process of fixation. 1.4. d) The axon of fresh nerve fibre sections which have been frozendried or fixed, contains filaments of indefinite length, with a diameter of 100–200 Å and regularly spaced axial discontinuities. These filaments show a predominantly longitudinal arrangement within the fibre and can aggregate to form compact bundles resembling neurofibrils. Dense oval corpuscles and clear vesicular bodies are also seen in the axon. 2. 2. In thin sections and dissociation preparations from the lateral funiculus of the frog and rat spinal cords, new types of submicroscopic fibres were found which have diameters ranging between 0.1 and 1 μ, and can be identified as nerve fibres by their connection with larger myelinated fibres and their fine structure. These fibres have regularly spaced fusiform enlargements occupied by dense bodies resembling Schwann nuclei, and consist of a thin sheath formed by a single tubular membrane, which contains long filaments 100 Å in diameter and a variable number of other structures. The finest fibres consist of a single membrane and only one central filament. The sheath membrane of these fibres is 60–80 Å thick and exhibits the same granular fine structure as the layered membranes of myelinated nerve fibres. 3. 3. Unmyelinated nerve fibres from the spinal cord and the sympathetic chains of frog and rat are constituted by compact bundles of nodose filaments, having a diameter of 100–200 Å and indefinite length, and are invested with a single granular membrane approximately 60–100 Å thick. Dense slender bodies resembling nuclei are attached to these membranes. 1. II. The findings presented here indicate that the structural elements of all types of nerve fibres are fundamentally similar, and point to a common pattern of organization in myelinated fibres of all sizes and in the so-called unmyelinated nerve fibres.

A Hitherto Undescribed form of Adult Axis in the Genus Batrachospermum

THE genus Batrachospermum has always attracted interest as one of the few freshwater members of the Florideæ and on account of its distinctive appearance. Notwithstanding a general familiarity with the external form and early development of Batrachospermum, it has not been recognized previously that the old axes of some species may appear "solid" in transverse section, either all or almost all trace of the primary central filament of cells being lost. Such a condition has been found to exist in three species of this genus (Fig. 1), and there is no reason for doubting that subsequent investigation may show it to occur in other non-ephemeral species. The three species mentioned have not been identified with certainty as comparison with type specimens has been impossible in present circumstances, but two undoubtedly belong to the Helminthoidea section of the genus. Only male plants of the third species, the one here illustrated, have been seen and hence its affinity remains in doubt.

The vibrations of an infinite system of vortex rings

The vibrations that may be set up and maintained in the central filament of a single vortex ring of small but finite section have been investi­gated by Thomson and others, but no corresponding investigation appears to have been undertaken for a system of parallel rings, although the matter is of some importance in connection with the state of motion behind a moving body. In a previous paper the authors have examined the stability of an infinite system of equal vortex rings situated in parallel planes with their centres evenly spaced along an infinite line and with their planes at right angles to that line. Instability was there found to occur for disturbances confined to displacements of the centre of each ring along the central axis, the filament of each ring still remaining circular. In the present paper the investigation is extended to deformation of the vortex filaments, and some interesting conclusions are drawn regarding natural modes of vibration of the infinite system of vortex rings, such as may occur without the longitudinal instability referred to in the previous paper becoming apparent. It is found, for example, that for any given ratio of radius of ring section to radius of ring there exists a critical ratio of ring spacing to radius, separating the region of stable oscillation from that of instability, a result in some respects closely analogous to that found by Kármán for the stability of two infinite parallel rows of rectilinear vortices.

Probleme der Protistenkunde

THE first of Prof. Doflein's studies, that on the Try-panosomata, was noticed in NATURE of June 24, 1909, p. 489. The present work deals with the Spirochaetæ, spirillar micro-organisms met with in ditch water and also in connection with many diseases, such as the relapsing fevers and syphilis, and as commensal parasites in the fresh-water mussel, &c. Some are doubtless vegetable in nature, but many must probably be regarded as belonging to the protozoa. From a critical survey of the minute structure of several species the author divides the spirochaetes into three groups: (1) Spiro-chaeta, with a central staining filament; (2) Cristispira, with a marginal staining filament; and (3) spirochaetes with a flattened band or lamella. He does not consider that sexually differentiated individuals have been proved to occur. The pathogenic forms, like many trypanosomes, are transmitted by blood-sucking arthropods, principally ticks. The essay is illustrated with many figures, and is a useful contribution to this important subject. Probleme der Protistenkunde. By Prof. F. Doflein Die Natur der Spirochaeten. Pp. vi + 36. (Jena: G. Fischer, 1911.) Price 1.20 marks.