The reactions which take place in cell protoplasm, as a result of the action of either physical or chemical stimuli, are accompanied by electrical disturbances, which may be either caused by, or the result of, changes in the electrical charges of the mineral salts which are present in the gel. Such changes, like the chemical reactions which they accompany, may be regarded as reversible and mutually self-regulatory; so that the protoplasm has not only the possibilities of enormous chemical reactivity, but also the mechanism for self-regulation of its actions, the products or results from any given series of changes generally tending to reverse the process by which they are proceeding and so to restore the condition of normal equilibrium.
Finally, the most characteristic difference between the reactions which go to make up the vital activities of a living cell and those of the same chemical substances when in inanimate form in the laboratory lies in the presence in the colloidal mass of the accelerating catalysts known as enzymes, which are produced by the protoplasm itself in some way which is as yet wholly unknown; and which not only add to the possibilities of rapid chemical change which are afforded by the colloidal nature of the material, but also, because of their extreme sensitiveness to minute changes in environmental conditions, serve to govern both the rate and the direction of the individual chemical reactions which constitute the vital activities of the protoplasmic mass. These enzymes are not distributed uniformly through any given cell, or organism, but are localized in different parts of the cell or tissue and so give to its different parts the ability to perform their various different functions.
References
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