Chapter VIII (part 5)

Reflex actions are simply responses by motion , reactions upon external irritations, taking place always in the same way, regardless p. 87 of their utility or futility, expediency or inexpediency in any given case. Their origin and laws are due to the simple irritability of a cell. What is the irritability of a cell, and what are these laws? The irritability of a cell is defined as its faculty to respond to external irritation by a motion. Experiments with the simplest mono-cellular organisms, have shown that this irritability acts according to definite laws. The cell responds by a motion to outside irritation. The force of the responsive motion increases as the force of the irritation is intensified, but in no definite proportionality. In order to provoke the responsive movement the irritation must be of a sufficient intensity. Each experienced irritation leaves a certain trace in the cell, making it more receptive to the new irritations. In this we see that the cell responds to the repetitive irritation of an equal force by a more forceful motion than the first one. And if the irritations be repeated further the cell will respond to them by more and more forceful motions, up to a certain limit. Having reached this limit the cell experiences fatigue , and responds to the same irritation by more and more feeble reactions. It is as if the cell becomes accustomed to the irritation. It becomes for the cell part of a constant environment , and it ceases to react, because it is reacting generally only to changes in conditions which are constant. If from the very beginning the irritation is so weak that it fails to provoke the responsive motion, it nevertheless leaves in the cell a certain invisible trace. This can be inferred from the fact that by repeating these weak irritations, the cell finally begins to react to them. Thus in the laws of irritability we observe, as it were, the beginnings of memory, fatigue, and habit. The cell produces the illusion, if not of a conscious and reasoning being, at any rate of a remembering being, habit-forming, and susceptible to fatigue. If we can be thus deceived by a cell, how much more liable are we to be deceived by the greater complexity of animal life. But let us return to the analysis of actions . By the reflex actions of an organism are meant actions in which either an entire organism or its separate parts acts as a cell , i.e., within the limits of the law of variability. We observe such actions both in men and in animals. A man shudders all over from unexpected cold, or p. 88 from a touch. His eyelids wink at the swift approach or touch of some object. The freely-hanging foot of a person in a sitting position moves forward if the leg be struck on the tendon below the knee. These movements proceed independently of consciousness, they may even proceed counter to consciousness. Usually consciousness registers them as accomplished facts. Moreover these movements are not at all governed by expediency. The foot moves forward in answer to the blow on the tendon even though a knife or a fire be in front of it. By instinctive actions are meant actions governed by expediency, but made without conscious selection or without conscious aim . They appear with the appearance of a sensuous tincture to sensations, i.e., from that moment when the sensation begins to be associated with a sense of pleasure or pain. As a matter of fact, before the dawn of human intellect, throughout the entire animal kingdom "actions" were governed by the tendency to receive or to retain pleasure, or to escape pain.