ELECTRON MICROSCOPIC OBSERVATIONS OF RAT AND MOUSE CEREBELLUM IN TISSUE CULTURE

Closely ordered stages of myelin formation in cultures of newborn rat and mouse cerebellum, selected by direct light microscopy, were studied with the electron microscope. Electron micrographs of these cultures reveal the presence of neurons, axons, neuroglia, microglia, and ependymal cells. The appearance of the neuron is identical to that previously described in vivo. The neuroglial cell has long, branching processes, and its cytoplasm is characterized by packets of long, narrow fibrils. During myelin formation, a glial cell process surrounds the axon. This process may form an internal mesaxon and may spiral for several turns around the axon. Other glial cell processes may interdigitate with or overlay the innermost process to contribute to the multilamellated structure. The glial processes flatten and the cytoplasmic surfaces of the cell membrane come into contact to form the lamellae of the myelin sheath. These adhesions may be temporarily incomplete as evidenced by sequestered islands of glial cytoplasm among the myelin lamellae. Ultimately, a compact, apparently spiral, myelin sheath is formed. These findings are discussed in relation to in vivo central myelin formation.     

Histoplasmosis in Montreal During the Fall of 1963, with Observations on Erythema Multiforme

Although Montreal is in an endemic area, significant clinical histoplasmosis with systemic manifestations has been, until recently, infrequently diagnosed. However, since the autumn of 1963, 31 cases of clinically significant histoplasmosis have been seen by the authors. These were divided into two groups: (1) patients in whom the diagnosis was established on the basis of histological and/or cultural demonstration of the fungus; (2) patients in whom the diagnosis was based on a positive histoplasmin skin test, a complement fixation antibody titre of 1:32 or greater and compatible clinical and radiological findings. An additional group of 11 patients who presented with erythema multiforme was investigated and a heretofore unrecognized relationship between histoplasmosis and erythema multiforme was established.     

STUDIES ON CELL DEFORMABILITY : I. Effect of Surface Charge

The deformability of the surface membranes of Sarcoma 37 and Ehrlich murine ascites tumor cells was assessed by the pressure required to suck a hemispherical bulge from these cells into a micropipette. It was shown that treatment with neuraminidase allowed the cells to be deformed with significantly less suction, and that enzymatic treatment also produced a significant reduction in surface charge as determined by measurement of cellular electrophoretic mobility. It is suggested that the increase in cellular deformability may be related to charge reduction, and that the charge at the cell periphery may affect not only the magnitude of the potential energy barriers hindering contact between cells, but also the ease with which cells can form low radius of curvature probes in order to help overcome these barriers.     

BONE BANKS—A New Concept in Procurement and Storage for Homologous Grafts

An unlimited supply of bones, obtained post-mortem and irradiated to make them sterile, is stored for as long as six months in a freezer, ready for use. After an immune response at first, bone thus treated is readily incorporated by the host in grafting procedures.     

Electron Microscopic Observations of the Carotid Body of the Cat

Carotid bodies were removed from cats, fixed in buffered 1 per cent osmic acid, embedded in deaerated, nitrogenated methacrylate, and cut into thin sections for electron microscopic study. The carotid body is seen to be composed of islands of chemoreceptor and sustentacular cells surrounded by wide irregular sinusoids. These cells are separated from the sinusoids by relatively broad interstitial spaces which are filled with collagen, fibroblasts, and many unmyelinated nerve fibers with their Schwann cell sheaths. The chemoreceptor cells are surrounded by the flattened, multiprocessed sustentacular cells which serve to convey the axons from an interstitial to a pericellular location. These sustentacular cells are assumed to be lemmoblastic in origin. Relatively few axons are seen to abut on the chemoreceptor cells. The cytoplasm of the chemoreceptor cell is characterized by numerous small mitochondria, units of granular endoplasmic reticulum, a small Golgi complex, and a variety of vesicles. There are many small vesicles diffusely scattered throughout the cytoplasm. In addition, there is a small number of dark-cored vesicles of the type which has been previously described in the adrenal medulla. These are usually associated with the Golgi complex. These findings are discussed in relation to the concepts of the origin of the chemoreceptor cell and the nature of the synapse.     

THE RESPONSE OF MALE GAMETES OF ALLOMYCES TO THE SEXUAL HORMONE SIRENIN

Attraction of male gametes of Allomyces to sirenin concentrations as low as 10^−-10 m has been demonstrated. Increasingly strong responses are observed to concentrations up to 10^−-6 m. The response is slightly weaker at 10^−-5 m and very weak at 10^−-4 m. Microscopic studies suggest that the attraction comes into the category of tropotaxis, a direct approach to a sirenin source occurring. Male gametes have been shown to inactivate sirenin. The possibility that this inactivation is an adaptation process enabling the gametes to maintain sirenin sensitivity over a 100,000-fold concentration range is discussed.