download PDF version - Dr Harold Hillman

We decided that we would look at fresh clumps directly, without any disruption orpreparation under phase contrast microscopy. It soon became obvious that they consisted almostentirely of mitochondria, similar to the appearance of mitochondria in neurons. We publishedthis (Hillman and Deutsch, 1978; Hillman, Deutsch, Allen and Sartory (1977). However, inrecent years, neuroglial clumps have disappeared from the literature. We concluded thatmitochondria and naked nuclei were the main constituents of the neuroglia, and occupied themajority of the volume of the brain and the spinal cord.While examining the literature, I came across an extraordinary anomaly in the electronmicroscopy of myelin lamellae. In every single publication, one saw an oblique view of acomplete myelin sheath, as judged by the long axis being significantly more than the short axis.However, the myelin sheath itself appears to be of uniform thickness all the way round even inthese obviously oblique sections. This observation appears to be true in every electronmicrograph in the literature. The only conclusion that one can come to about this is that theimage at which one is looking is two-dimensional, that is to say, that it arose after the sectionwas cut.Furthermore, in unfixed myelin sheaths, viewed by phase contrast microscopy, therefractive index of the sheath appears higher than that of the axons. If the myelin sheath werecomposed of scrolls of Schwann cell membranes, as indicated by the Geren model (1954), onewould expect the refractive index of the myelin sheath to be higher.High power light microscopy allows one to see Brownian movement of particles in themyelin sheaths (Singer and Bryant, 1969). This would not be possible, if the myelin sheath weresolid with lamellae.Consequences of proposed new cellular structure33