The mind in daily life / by R.D. Gillespie ; with nine diagrams.

  • Gillespie, R. D. (Robert Dick), 1897-1945.
Date:
1933
Catalogue details

Licence: In copyright

Credit: The mind in daily life / by R.D. Gillespie ; with nine diagrams. Source: Wellcome Collection.

    133/306 (page 125)
    Fatigue follows exercise ; but in a nerve fibre itself it is a matter of the greatest technical difficulty to demonstrate any change at all as the result of exercise. This has lately been done, however, for at least certain non-medullated nerve fibres. (Medullated fibres, i.e. those possessing a sheath, compose the central nervous system. Certain nerve-fibres outside the brain and spinal cord do not possess a sheath.) But the energy change is so extremely small that on this and other grounds it can safely be assumed that nerve fibre itself, of which the bulk of the brain and spinal cord are composed, is practically indefatigable. It is otherwise, however, with the nerve cells. There is evidence—indirect evidence, it is true—of the fatiguability of nerve cells. It has been ob¬ served that after, for example, excessive exercise of the cells having fibres connected with muscles, the cells have lost much of their stainable substance ; this is presumptive of the fatigue of the cells, in the sense of a diminished capacity for work. But what matters in real life is not the cell nor the fibre, but the whole collection of cells and fibres comprising the nervous system. To obtain direct experimental evidence of fatigue of the latter is not at all easy. Experiments have shown that muscular exercise consumes enormous amounts of energy, as measured by the alteration of the ‘ metabolic rate ’ (rate of exchange of oxygen and carbon dioxide) : but similar experiments directed to discovering the energy con¬ sumption of the entire organism during purely mental work have failed to discover any metabolic alteration at all. The energy change involved in mental work must therefore be very small. Recently a new direct method has been devised, which consists in measuring the relative amounts of oxygen and carbon dioxide in the carotid artery (supplying the brain) and the jugular vein (draining the brain). A diminution in oxygen and glucose and an increase in carbon dioxide has been demonstrated in the jugular blood, indicating a utiliza¬ tion of energy in the brain tissues ; but it remains to demon¬ strate an increased consumption of oxygen during mental work. Probably any such increase will be very small indeed. Collateral evidence comes from an entirely different line of