The human brain : its structure, physiology and diseases. With a description of the typical forms of brain in the animal kingdom / by Samuel Solly.

Date:
1847
Catalogue details

Licence: Public Domain Mark

Credit: The human brain : its structure, physiology and diseases. With a description of the typical forms of brain in the animal kingdom / by Samuel Solly. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    51/736 (page 23)
    fibres. 4th, In the nerves of involuntary muscles, and of the less sensitive or insensible mucous membranes, there is a great preponderance of fine fibres.^ From the above facts, it may be concluded that nerve- fibres of the sympathetic nerve differ from those of cerebro- spinal, in the absence of the white substance of Schwann ; and this substance is found where the nerve is more exposed to pressm^e or any kind of injury from external causes. When the filaments of the cerebro-spinal have nearly reached their destination, then they cease to require the protecting material which was necessary in their course down a limb, and between the bodies of the muscles. The sympathetic nerve is generally deep-seated and well pro- tected, and hence the absence of this protecting matter. We can easily understand what contrivance must be necessary to protect the delicate neurine when it has to travel, like the sciatic nerve, for instance, from the pelvis to the toes. Physically it appears almost as strong as a tendon, and it had need to be so, exposed as it is in all the movements of the limb. Its physical strength, then, and its power of resisting injury, is due to its investing membrane and the presence of the matter of Schwann; while the essential portion of the nerve, that in which its vital powers reside, is the axis cylinder. We all know that even with all this bountiful provision, the nerves may be easily compressed so as temporarily to suspend their function. If we only fall asleep with one leg crossed over the knee of the other, so as to compress the popliteal nerve, when we awake we find our leg numb and powerless, until we have suffered all the pain of the feeling commonly called pins and needles, or live blood, as the nerve-fibres recover their power, and the nervous current is re- established. Sometimes when you are examining the nerve- tubes under the microscope, from the spinal cord of the frog, you will see the two kinds of tubes most distinct. The accompanying figm-e represents two of the * British and Foreign Quarterly Medical Eeview, p. 273. Fig. Gelatinous nerve- fibres in the frog.