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Page:Popular Science Monthly Volume 24.djvu/788

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cal and physical forces for those proximate constituents which go to nourish and build up the tissues and enable the organs of the body to perform their respective functions.

In nutrient action, by which lifeless material or pabulum is transformed into living tissues, evidence of this vital entity should be discovered, if anywhere, for here we have the primal seat of life, the very fountain of genetic power.

Analysis, however, finds room for it in nutrient action no more than in the mysteries which lie concealed in every expression of energy throughout nature's domain. Why will friction of glass produce a condition or property which will repel pith-balls, while friction of sealing-wax produces a condition which will attract them? Are these movements caused by some kind of life-principle developed in so simple a way? No; they come from positive and negative electricity evolved by friction, and, with this answer, science asserts that the explanation is complete. When asked, What is electricity, beyond a special display of energy? there is no answer.

If we question the various organic functions of the body, physical and chemical forces alone confront us. A muscle contracts according to mechanical laws, and its work is expressed in mechanical equivalents. Electric tension is lost, heat is evolved, carbon dioxide appears, and the muscular tissue, before neutral in reaction, is now acid. Whatever may be the nature of the vital force, if such there be, operating in muscular contraction, it at least is not independent of physical and chemical forces, and the evidence is cumulative that these will alone explain the phenomenon. Respiration is purely a chemical process, in harmony with the laws of gaseous diffusion. Circulation, with its pumps, pipes, and valves, is an hydraulic operation. Absorption is osmotic, and a similar selective affinity for special things is exhibited in inorganic material as well as in animal membranes.

There seems no good reason why we should hesitate to regard the vital force as correlated with the physical forces known to us as heat, light, electricity, and actinism. That some relation exists there can be no doubt, for the effect of physical forces upon organic life is marked, and their energy is made potential in the tissues of both vegetables and animals. This potential energy is, after a time, transformed into active energy, and new phenomena result.

Organic forms do not generate energy, they simply transform or evolve it from that which has been supplied from the outer world. Heat in the body results from combustion the same as in a furnace.

Contractility is a special function of muscular tissue, and is independent of nerve-force. This attribute exists in the tissue for a time after death, lasting longer in cold-blooded than in warm-blooded animals, because of the slowness of the process of the destructive assimilation of the tissues. Longet demonstrated that contractility is closely related to the supply of arterial blood in the capillary vessels, for, on