Abstract
Our only direct intimation of the existence of space is the sensation of vertigo, when through our cortical centres we become conscious of the fact that we are surrounded by a “blank” space in which motion is apparent, i.e., the relative condition of our body to the things around us seems to be altered. A precise account of the “nerve-cycle” and of its exact relation to the sympathic and parasympathic—in a word, to the autonomous vegetative—system and to the endocrine system, is at present impossible. We have known since the time of the classic investigations of Flourens, Breuer, Mach, Crum Brown, and their followers—especially Sherrington—that the nature of these things is highly complicated. Simple mechanical theories are useless, even for teaching purposes, as they are more or less fictitious and often incomplete.
The path of nervous action is through the ear, cerebellum, brain stem, cerebrum, medulla oblongata, spinal cord, and autonomous nervous system, to the different parts of the periphery, and there are also mutual connexions with the endocrine glands. Mention is made of the influence of constitution (i.e., inheritance, “the natural endowment”), and also of the conditional disposition, temper, training, in a word all external and internal stimuli. Again, the various reflexes, the numerous aggregations of ganglia, indicating a certain autonomy of function, constitute a great problem for future clinical observation. The mechanism of adaptation and compensation by which extensive injury may sometimes be counterbalanced, also enters into the question, as do the varying collateral paths, the synergetic action of different and sometimes very distant organs and so forth. Again, we have to think of the ratio of irritability and fatiguability, a significant factor in causation. Syphilis, arthritis, alcoholism, nicotine-poisoning, anæmia, leukæmia, tumours, and—especially—catarrh, are most important causes.