When groping in the dim recesses of memory, we always perceive that there are associations and intimate connections amongst the phenomena of thought. The blood, making its way into certain parts of the brain, is like the light of a torch penetrating subterranean passages, on the walls of which are painted pictures of things we know. Often the blood-vessels do not yield, and we then wander in vain in that labyrinth, retracing our steps, roaming hither and thither, until suddenly we see an opening, and what we were seeking appears unexpectedly before us. The supposition that we here have to do with an effect of the blood, an expansion or contraction of the vessels, and with phenomena of nutrition, seems to be strengthened by the circumstance that sometimes, in consequence of violent emotion, a succession of things which before seemed totally forgotten suddenly reappears in our memory. The link between physical phenomena and phenomena of memory is more apparent during fatigue and the refreshing state of repose. Memory may fail entirely from anæmia, from poisoning by narcotics, innutrition of the brain, and in old age; for we all know how much better we remember the events of our youth than those of later occurrence. Men who have had wounds or contusions on the head have been known to forget that they had children; authors have forgotten even the titles of their works; but as soon as the fever had passed, or the wound healed, they regained their memory. Others, during a fever, have related events and remembered names which they had quite forgotten previously, and which they were unable to recall after recovery. CHAPTER II _REFLEX ACTION AND THE FUNCTIONS OF THE SPINAL CORD_ I Until 1820 physiologists believed that all nerves had the same functions; that is, that all were sensory. We can scarcely picture the confusion in the mind of anyone studying the nerves of the face when, besides those destined to the organs of smell, sight, and hearing, he would notice two other large nerves--the Trigeminus and Facialis--passing off separately from the brain and spinal marrow, and which, with a double ramification of filaments, cover all superficial and underlying parts of the face; and again, when he saw the three nerves of various origin which go to the tongue, the four which are distributed in the throat, and finally, in the midst of this net of nerves, thick bundles of fine filaments and ganglia of which the origin was untraceable.