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.The true source of its functional capacity lies, however, notin these, but in the chemical compounds of which nerve-mass and contractile substance are composed, andwhich are taken over, almost without modification, from the living laboratory of plant-tissue.These containthe store of potential work, which under the influence of external stimulation is transformed into actual work.The compounds of which the nerve-mass consists remain, so long as stimulus-processes do not intervene tomodify them, approximately in that stationary condition which appears to outward observation as a state ofrest.This rest is, however, here, as in all such instances of a stationary condition, only apparent.The atoms ofthe complex chemical compounds are in continual motion; now and again, they travel beyond the sphere ofoperations of the atoms with which they have hitherto been combined, and come within that of other atoms,freed like themselves.There is, therefore, in a liquid so easily decomposable as the nerve-mass, a constantalternation of decomposition and recomposition of chemical compounds, and the mass appears stationarysimply for the reason that, on the average, there are as many processes of the one kind going on as of theother.In this particular instance, however, we cannot in strictness say even so much: not even during theirperiod of rest is the state of the nervous elements really constant and unchanged.With compounds of suchCHAPTER III.Physiological Mechanics of Nerve-Substance 41 Principles of Physiological Psychologycomplexity, it invariably happens that certain of the atoms which have been removed from their formersphere of operations do not, in reuniting, enter into their old connexions, or into connexions of the sameorder, but combine afresh to form similar and more stable compound.This process is termed intrinsicdecomposition.In the living organism the disturbances arising from intrinsic decomposition are compensatedby the removal of the products of decomposition, and by the intake of new materials for the renewal of theconstituents of the tissues.We may, then, consider resting nervous substance as a semisolid mass given in a stationary condition ofmotion.In such a mass, there is no release of external work; the work values produced by the individualatoms cancel one another.This cancellation takes place, in large measure, within the complex chemicalmolecules.As the atoms of the molecule oscillate about their positions of equilibrium, each one of them doesa certain work, which, however, is counteracted by the work of other atoms, and consequently is notperceptible outside the molecule.This internal molecular work is far more considerable in an instablechemical compound, owing to the greater freedom of movement possessed by the atoms, than it is in a stablecompound.It is this, therefore, that represents the potential work of the compound.For if the existing state ofequilibrium be disturbed, the relatively instable may pass into a relatively stable compound; in which eventthe surplus of internal molecular work contained in the former is at once transformed into external.To acertain extent, however, the establishment of equilibrium takes place without the chemical molecule.Whereatoms are continually passing from less stable to more stable connexions, work must appear: where, on theother hand, atoms are transferred from more stable to less stable connexions, work must correspondinglydisappear: and in both cases it is external molecular work, generally heat, that is produced and consumedagain.We may term the work that appears with the origination of the more stable compound 'positive'molecular work, and the work that disappears with the formation of the less stable compound, 'negative'molecular work
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