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The structure of the membranes of sarcoplasmic reticulum (SR), tubular (T) system, and sarcolemma has been studied by freeze fracture in leg muscles of the Tarantula spider. Two regions of the sarcoplasmic reticulum can be differentiated by the distribution of particles on the fracture faces: a junctional SR, at the dyads, and a longitudinal SR, elsewhere. The dyads are asymmetric junctions, the disposition of particles in the apposed membranes of SR and T tubules being different from one another and from the regular arrangement of feet in the junctional gap. It is concluded that no channels can be visualized to directly connect SR- and T-system lumina.

Sulla base delle conoscenze recentemente acquisite sulla struttura delle miche triottaedriche si propone per le biotiti una nuova curva teorica che permette la determinazione ai raggi X del numA-o di atomi di Mg e di Fe in posizione ettaedrica. La determinazione è basata sull'uso delle intensità relative delle diffrazioni 004, 005, 006. Si ritiene che l'errore in tale determinazione non sia superiore a ± 0.5 atomi di Fe o di Mg su sei posizioni ettaedriche.

Striated muscle fibers from the body and tail myotomes of a fish, the black Mollie, have been examined with particular attention to the sarcoplasmic reticulum (SR) and transverse tubular (or T) system. The material was fixed in osmium tetroxide and in glutaraldehyde, and the images provided by the two kinds of fixatives were compared. Glutaraldehyde fixes a fine structure that is broadly comparable with that preserved by osmium tetroxide alone but differs in some significant details. Especially significant improvements were obtained in the preservation of the T system, that is, the system of small tubules that pervades the fiber at every Z line or A-I junction level. As a result of this improved glutaraldehyde fixation, the T system is now clearly defined as an entity of fine structure distinct from the SR but uniquely associated with the SR and myofibrils. Glutaraldehyde fixation also reveals that the T system is a sarcolemmal derivative that retains its continuity with the sarcolemma and limits a space that is in direct communication with the extracellular environment. These structural features favor the conclusion that the T system plays a prominent role in the fast intracellular conduction of the excitatory impulse. The preservation of other elements of muscle fine structure, including the myofibrils, seems for reasons discussed, to be substantially improved by glutaraldehyde.

A simple method for the analysis of bubble chamber pictures is described. It is sufficiently precise for most works and has been succesfully used during the last year. Some details of practical interest are included.

A rapid cycling bubble chamber is used to measure the polarization of the recoil proton from the reaction γ+p→π0+p. The experimental setup and the method of analysis of the events are described. We give a preliminary result of the polarization for a mean photon energyk=725 MeV and a center of mass angle of 87°.

L’idrogeno occluso nei metalli, sopratutto nel palladio, è facilmente spostabile per mezzo di forze di natura diversa, così da lasciar prevedere la possibilità di una azione della centrifugazione del metallo idrogenato, sull’idrogeno occluso.

È confrontata la diffusibilità relativa dei due isotopi dell’idrogeno nel palladio e Vinfluenza di un campo elettrico applicato al metallo sullo spostamento in esso del deuterio.

The structure of the triadic junction in frog slow fibers has been studied and compared with that of twitch fibers. The junctional gap is wider (by approximately 13%) in slow fibers. The junctional feet have the same size and disposition as in twitch fibers, although the size and shape of the junctional areas are different. It is concluded that the role of triads in slow fibers is the same as in twitch fibers

The structural simplicity of the Z line in fish muscle fibers allows direct visualization of its basic geometry. Models which postulate termination of the I filaments at the edges of the Z line and the direct linkage of I filaments belonging to the two adjacent sarcomeres by Z filaments crossing the whole width of the Z line give the best fit to the electron micrographs. The structure of fish Z lines is not significantly altered by the use of different fixation procedures and by changes in sarcomere length.

Cytometric researches were carried out on liver of albino mice (mus musculus) of six different strains in order to study the cytoplasm-nucleus ratio. The examinations were performed at the following age after birth: 12 hours, 8 days, 33 days, 3 months, 1 year, 2 years. « Mipro 3 » microscope was used; the sections were stained by hematoxylin-eosin and by the Lillie method (allochromatic method). A gradual increase of the cytoplasm-nucleus ratio was observed according to the age. The highest values of this relation were found after 1 year of age.

A coarse-grained, colourless lepidolite from a pegmatite of the Elba Island (Italy) has been examined. X-ray powder-diffraction and single-crystal patterns reveal the presence of the 1M and 2M2 polymorphs, for wich cell parameters are given. On the basis of the optical and X-ray data the same composition for both the polymorphs is inferred. From the chemical analysis data of the whole micaceous material the following formula has been computed: (Ca0,01Na0,06K0,92Rb0,06) (Al1,27Mg0,01Li1,75) (Si3,36Al0,64)O10 (F1,53OH0,47). The crystal structure of this mica has been studied by means of one-dimensional Fourier projections on c* and several interesting structural parameters were derived. Among them the mean tetrahedral rotation results to be about 11° for both the polymorphs: a value (quite similar to those of the other trioctahedral micas with K+ as interlayer cation) wich does not confirm Radoslovich's hypothesis that lepidolites should have a symmetry of the tetrahedral layers very close to the perfect hexagonality. Finally a new hypothesis on the structure of the 2M2 polymorph consistent with such a proved ditrigonal symmetry of the basal oxygens arrangement in the lepidolites is pointed out.

A study, mainly by electron microscopy, has been made on two leg muscles of rat, in the course of atrophy experimentally induced by total denervation. As a preliminary the chief distinctive features of the soleus, chosen as a representative of pure red muscle, and of the gastrocnemius, representative of pure white muscle, are described. Two major phases of atrophy, somewhat overlapping in time, were observed. In the first, a degenerative autolytic process takes place in areas of the fiber, with loss of striation. It can be detected as early as the 7th day, but the maximum is observed at the 14th day, and accounts for a gross weight loss of 50 per cent. The first alteration appears in the Z lines; disorder in the disposition of filaments then follows. The process occurs very rapidly, leaving large areas in the cell in which one can detect only ground substance, glycogen, rare randomly disposed vesicular elements, and some mitochondria. Several lysosomes and masses of lipoproteins, which assume the configuration of concentric lamellae, show up in these fibers. Subsequently large parts of the waste sarcoplasm are discarded into the intercellular spaces. In the second major phase the so called "simple" atrophy takes place. The process starts early, but its effects are more detectable after 1 month. In this period, single myofibrils undergo different degrees of reduction in diameter, while the spatial disposition of primary and secondary filaments inside the fibrils remains normal. The appearance of the fibrils in longitudinal sections suggests that the process takes place by the detachment of filaments from the periphery of the fibrils and by their subsequent breakdown in the interfibrillary spaces. The sarcoplasmic reticulum is still well preserved, and relatively overdeveloped. Mitochondria disappear in parallel with the contractile material.