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That this nerve mechanism may effectively carry out its twofold function, first, of self-adaptation to meet adequately the increasingly complicated stimuli of environment; and second, of adapting the motor mechanism to respond adequately to its demands, there have been implanted in the body numerous nerve ceptors some for the transmission of stimuli harmful to the mechanism nociceptors some of a beneficial character beneceptors; and still others more highly specialized, which partake of the nature of both bene- and nociceptors the distance ceptors, or special senses.

Each brain pattern is adapted for but one type of motion, and so the specific stimuli of the innumerable ceptors play each upon its own brain pattern only. In addition, each brain pattern can react to stimuli applied only within certain limits. Too bright a light blinds; too loud a sound deafens.

Stimuli of the contact ceptors differ from stimuli of the distance ceptors in still another important particular. The adequacy of stimuli of the contact ceptors depends upon their number and intensity, while the adequacy of the stimuli of the distance ceptors depends upon the EXPERIENCE of the species and of the individual.

Walking, running, and their modifications constitute an adaptation of wonderful perfection, for, as Sherrington has shown, the adaptation of locomotion consists of a series of reflexes ceptors in the joints, in the limb, and in the foot being stimulated by variations in pressure.

When, however, stimuli of the distance ceptors compete with stimuli of the contact ceptors, the contact-ceptor stimuli often secure the common path, not because they are stronger or more important, but because they are immediate and urgent.

But if all the pain nerve ceptors but one were equally stimulated, and this one more strongly stimulated than the rest, then this one would gain possession of the final common path would cause a muscular action and the sensation of pain. It is well known that when a greater pain or stimulus is thrown into competition with a lesser one, the lesser is submerged.

The distance ceptors, on the other hand, adapt man to his distant environment by means of communication through unseen forces ethereal vibrations produce sight; air waves produce sound; microscopic particles of matter produce smell.

Concentration is but another name for a final common path secured by the repetition and summation of certain stimuli. If our premises are sustained, then we can recognize in man no will, no ego, no possibility for spontaneous action, for every action must be a response to the stimuli of contact or distance ceptors, or to their recall through associative memory.

This postulate applies to all kinds of pain, whatever their cause whether physical injury, pyogenic infection, the obstruction of hollow viscera, childbirth, etc. All forms of pain are associated with muscular action, and as in every other stimulation of the ceptors, each kind of pain is specific to the causative stimuli.

Thus through the innumerable symbols supplied by environment the distance ceptors drive this or that animal according to the type of brain pattern and the particular state of threshold which has been developed in that animal by its phylogenetic and ontogenetic experiences. The brain pattern depends upon his phylogeny, the state of threshold upon his ontogeny.