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First of all, it is found that the nervous system has a certain up-and-down arrangement from the segments of the spinal cord up to the gray matter of the rind or "cortex" of the large masses or hemispheres in the skull, to which the word brain is popularly applied. This up-and-down arrangement shows three so-called "levels" of function.
The nutrient artery, after entering the medullary canal through a special foramen in the cortex, bifurcates, and one main division runs towards each of the extremities, and terminates at the ossifying junction in a series of capillary loops projected against the epiphysial cartilage.
They are dependent upon the modificability of nerve cells and fibers by stimuli, e. g., a light flashing through the pupil and passing along the optical tracts to the occipital cortex produces changes which constitute the basis of visual memory. Experience modifies nervous tissue in definite manner, and SOMETHING remembers. Who remembers? Who is conscious?
The motor cells of this middle level also discharge into the motor mechanisms of the lowest level. Jackson located these middle level structures in the cortex of the central convolutions, the basal ganglia and the centers of the special senses in the cortex.
It is also stated that only young pines are badly attacked by this form: it is rare to find Æcidia on trees more than twenty years or so old. The epidermis is already ruptured at p by the pressure of the young Æcidium. Much more disastrous results can be traced directly to the action of the mycelium in the cortex.
They are perpetually shed from the surfaces of solids, as bark is shed by trees. Cortex is, indeed, one of the names applied to them by Lucretius. These evanescent films may be seen in one of their aspects in any clear, calm sheet of water, in a mirror, in the eye of an animal by one who looks at it in front, but better still by the consciousness behind the eye in the ordinary act of vision.
In addition to this general demarcation of functions as higher and lower first, second, and third level in their anatomical seat, many interesting discoveries have been made in the localization of the simpler functions in the cortex itself. The areas marked out are in general the same on both hemispheres, and that is to say that most of the centres are duplicated.
He now proposes to thrust us into a larger and much more intricate sphere of activity as to the representation in the cortex of other changes which as he has described are inframicroscopical or inframacroscopical. In other words, there must be some type of correlation between the projection in the cerebral structure of the organ itself which is cerebrally represented and certain mental signs.
Various ideas of movements to be carried out are struggling for control in the cortex of the brain. That is the normal status which precedes any decision. The channels of motor discharge are open for both possibilities; we may turn to the right or to the left. Then the play of associations begins. A larger and larger circle of ideas surrounds the idea of the one and of the other goal.
Mechanical pressure on the cortex of the brain can bring this state of things about, even as it can convert a saint of God into a devil incarnate. Was Berselius under the influence of forced amendment of this sort? Adams was not even considering the matter, he was lost in gloomy thoughts.
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