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Page:Popular Science Monthly Volume 4.djvu/123

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ably ever remain so. The nature of the union is a mystery, just as the nature of the union between gravity and matter is a mystery; in both cases we investigate only the laws of the phenomena. As the problem is one of the connection between two systems of action, the first step toward its solution must be to resolve these two systems into their simplest elements. The structural elements of the nervous system are marvelously simple; they consist of microscopic cells and fibres, the former being seats or centres of force, and the latter being the means of transmitting it.

Cells and fibres are the instruments of mental action, and, exactly as we rise in the scale of intelligence in animated creatures, there is an increase in the mass of the nervous centres—that is, a multiplication of the nerves and fibres which constitute them. In man, the most intelligent of the animal series, the organ of intelligence is relatively very large, and attains the highest degree of complexity.

Prof. Bain represents the nervous elements of the human brain as follows: "The thin cake of gray substance surrounding the hemispheres of the brain, and extended into many doublings by the furrowed or convoluted structure, is somewhat difficult to measure. It has been estimated at upward of 300 square inches, or as nearly equal to a square surface of 18 inches in the side. Its thickness is variable, but, on an average, it may be stated at one-tenth of an inch. It is the largest accumulation of gray matter in the body. It is made up of several layers of gray substance divided by layers of white substance. The gray substance is a nearly compact mass of corpuscles of variable size. The large caudate nerve-cells are mingled with very small corpuscles less than the thousandth of an inch in diameter. Allowing for intervals, we may suppose that a linear row of 500 cells occupies an inch, thus giving 250,000 to the square inch for 300 inches. If one-half of the thickness of the layer is made up of fibres, the corpuscles or cells, taken by themselves, would be a mass one-twentieth of an inch thick, say 16 cells in the depth. Multiplying these numbers together, we should reach a total of 1,200,000,000 cells in the gray covering of the hemispheres. As every cell is united with at least two fibres, often many more, we may multiply this number by four for the number of connecting fibres attached to the mass, which gives 4,800,000,000 fibres."

Now, in saying that such a wonderful organism as this is the seat and embodiment of the mind, we require to give distinctness to our conceptions, and are compelled to regard the connected cells and fibres as the simple instruments of simple mental processes as the whole fabric is the organ and measure of the whole mind. The corporeal elements are cells and fibres—what are the psychical elements in their lowest analysis? The old division of of the mind into faculties—as reason, judgment, memory, and imagination—is insufficient, for these are far from being ultimate elementary processes, but are rather the most complex actions of the collective forces of the intelligence in different modes of exercise. The later psychology resolves all these so-called faculties into a few constituents which form, if we may so speak, the contexture of the intellect. As Prof. Bain remarks: "We have no power of memory in radical separation from the power of reason or the power of imagination. The classification is tainted with the fault called in logic 'cross-division.' The really fundamental separation of the powers of the intellect is into three facts, called: 1. Discrimination, the sense, feeling, or consciousness, of difference; 2. Similarity, the sense, feeling, or consciousness, of agreement; and, 3. Retentiveness, or the power of memory or ac-