Nerves, master-system of the body / by David Fraser-Harris.

  • David Fraser Fraser-Harris
Date:
1927
Catalogue details

Licence: In copyright

Credit: Nerves, master-system of the body / by David Fraser-Harris. Source: Wellcome Collection.

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    The largest nerve in the body, the great sciatic in the thigh, is about as thick as a man’s thumb; the others vary in size down to mere threads. If we cut out a short piece of nerve and tear it to pieces with a couple of needles, we can make out under the microscope an immense number of very long, very narrow, opaque, whitish threads. Each of these is a nerve- fibre. We call them “ microscopic ” ; but that description applies only to their width, for their length may be one, two, or even three feet. Since the nerves for muscles extend all the way from the spinal cord to the remotest muscle, the nerve to the muscles of the great toe could easily be three feet long in a man of six feet. In order to make out any more of the struc¬ ture of a nerve-fibre, we require to put the nerve through a long series of chemical processes known as “fixing and staining”, before it can be cut into slices thin enough for microscopic examination. When this has been done, we see that each fibre consists of a minute cylinder the centre of which is occupied by a strand of delicate nerve-protoplasm (the axis- cylinder process) surrounded by a sheath of fatty material (the medullary sheath) outside of which there is a second but extremely thin sheath called the neurilemma. Fig. 3 shows