Many have thought and asserted, because the muscles and glands of our body grow heated by their work, that the brain and nerves also grew warm during activity. For my part, I doubt the accuracy of the methods used in these experiments, nor shall I be convinced unless it be clearly shown to be a fact. As the nature of the chemical processes taking place in the brain is totally unknown to us, it may be that the brain grows colder during activity. The question can only be decided when we succeed in eliminating the serious complications which the greater flow of blood produces in such cases.
Till the present day no one knows what parts of the brain are consumed in order to produce thought; no one can imagine how the molecules of the blood penetrate the mass of cerebral cells and become part of consciousness, and neither do we know how, from the joint life of the single cells, something can arise which represents consciousness and sensitivity.
Doctrines are here of no use. When our mind has arrived at the last division of matter, at the last localisation of psychic processes, we feel that it is vain to say we are materialists or spiritualists. All schools are confounded in the nullity of our ignorance. The nature of matter is as incomprehensible as that of spirit. From Lucretius, who gave thirty proofs to demonstrate the materiality of the soul, down to modern materialists, not one step has been taken towards the discovery of the nature of thought. As a matter of fact, many materialists throw down one dogma and build another out of its ruins.
If we reject the hypothesis of the spiritualists, we must, with the same severity, banish from the borders of experimental science those who, in our time, wish to explain, by means of materialistic doctrines, the mechanism generating thought. Anatomy and physiology, the knowledge of structure and of cerebral functions, have scarcely lisped their first words, and dense darkness reigns over the nature of nervous processes, over the physical and chemical movements animating the hidden parts where consciousness has its throne. Let us speak neither of spirit nor of matter; let us candidly acknowledge our ignorance. We trust to the future of science and persevere in the search after truth.
CHAPTER V
PALLOR AND BLUSHING
I
Man has, on the average, four kilograms of blood, and this fluid flows incessantly in a system of tubes, in the centre of which the heart is situated. The arteries carrying the blood from the heart to the surface divide into many branches, separate, extend, and visit all parts of the body, feeding and irrigating them. When the ramifications of the arteries become so small that the eye can no longer see them, as, for instance, in the lips, the finger-tips, the cheeks, the ears, or any part of the skin, they take the name of capillaries. This is meant to indicate that these little arteries are as fine as a hair, but in reality they are very much finer. These last closely connected capillary nets give the skin its beautiful rosy colour. But however much they diminish, dividing and subdividing ad infinitum, they still form a system of canals, with walls and closed on all sides. There must be a wound, a cut, or a contusion, before the blood oozes out of these little vessels. Out of the capillaries the blood passes into larger canals called veins. Several veins flowing into each other form a bigger vein; in the same way as a brook is formed by springs, as the brooks, running into each other, form a rivulet, and the rivulets, a river; so the veins gradually receive the blood in larger streams, until at last they carry it in the great trunk-veins to the heart, which drives it again into the arteries.