atmospheric air with the combustible fuel in the furnace, produced the heat and force of the engine; but he did not know that in living bodies there is going on, only more slowly, a similar combination of the oxygen of the air with the like combustible matter in the food, as this circulates after digestion in the form of blood through the lungs, which combination produces the warmth and force of the living animal. The chief resemblances of the two objects are exhibited strikingly in the following table of comparison, where, in two adjoining columns, are set forth nearly the same things and actions, with difference only in the names:

LIFE NOT A PECULIAR PRINCIPLE.

9

8. A deficiency of fuel, water, or air, first disturbs, and then stops the motion.

9. Local damage from violence in a machine is repaired by the makers.*

8. A deficiency of food, drink, or breath, first disturbs, then stops the motion and the life.

9. Local hurt or disease in a living body is repaired or cured by the action of internal power given by the Creator.

We have here illustrated the mode only in which the force in animals is generated; the form it ultimately takes depends entirely upon the organization through which it has to pass. Life was thought to be a peculiar principle; but it depends for its development and manifestation entirely upon the union of the ordinary physical forces with a peculiar structure or arrangement of forces; for what are called vital forces are only the correlate of physical forces.

In a very small part of the acorn lies the structure that can develop only into an oak, and the human germ, in which lie folded up the wondrous powers of man, is invisible without the aid of the microscope. Life then is only Force acting through special organizations, which organizations, so far as we yet know, are formed only by transmission from parent to offspring; they are always hereditary.

66

But seeds might remain for ever unchanged-as the wheat in the pyramids, for 3,000 years, until quickened into being by forces from without. Thus, for example, when a seed is placed in the ground, the first process which takes place within it is one of decomposition. The mass of the seed consists of starch and albumen, in the midst of which is placed a small cellular body, called the germ. This germ will grow, and develop into the future plant, but only on condition that a process of decay goes on in the starchy and albuminous matter with which it is in connection. Part of

* A Survey of Human Progress, p. 159.

the latter sinks into the inorganic state, uniting with oxygen, and passing off as carbonic acid. The young plant is at first of less weight than the seed or root which has disappeared in generating it. When it arrives at the surface of the soil, a new process commences. The rays of the sun, falling on its leaves, maintain in them a continuance of the same process (one of chemical change) by which the first development of the germ was determined. Thus new materials are added to the plant, the light exciting those chemical processes which produce the organic arrangement of fresh portions of matter. The leaves, under the stimulus of the sun's rays, decompose carbonic acid, giving off part of the oxygen, and 'fix,' as it is said, the carbon in union with hydrogen, and sometimes with nitrogen, &c., to form the various vegetable cells and their contents.

"An animal now consumes this plant. In digestion there takes place again a precisely similar process to that with which we started-the germination of the seed. The substance of the plant partially decomposes; a portion of it sinks into a state approximating to the inorganic, while another portion (doubtless by means of the force thus generated) becomes more highly vitalized, and fitted to form part of the animal structure. The germination of the seed, and animal digestion, are parallel processes. Each of them is two-fold-a decomposing and a vitalizing action going on together, the latter having its origin in and depending on the other. Having formed part of the animal structure for a time, this living matter decomposes yet again, and again gives off its force. But now, instead of effecting, as in the previous cases, a vitalizing action, the force produces a mechanical action in the muscles, or a nervous action in the brain, or, in short, the function of whatever organ the matter we are tracing may have been incorporated with;-the

function being but another mode of operation of the same force which caused the nutrition. And thus, supposing the action to have been a muscular exertion, say the lifting of a weight, we shall have traced the force, which came from the inorganic world at first, in the form of the sun's rays, and was embodied in the substance of the plant, back again into the inorganic world in the form of motion. * * * The plant yields up its life to nourish the animal body, as that body, so nourished, in its activity yields up its life to impart force to the world around. * * ** Every giving off of force has for its necessary effect the storing up of force in The two halves of this process

equal amount elsewhere.

cannot be divided.”* †

Physiological Riddles. Cornhill Magazine.

There is an admirable paper on "Vitality", illustrating this subject, in the "Reader" of October 29th, 1864, signed "J. T.”, evidently Professor Tyndall. As the subject is of so much importance we make no apology for quoting at some length.

In what sense, then, is the sun to be regarded as the origin of the energy derivable from plants and animals? Let us try to give an intelligible answer to this question. Water may be raised from the sea-level to a high elevation, and then permitted to descend. In descending it may be made to assume various forms-to fall in cascades, to spurt in fountains, to boil in eddies, or to flow tranquilly along a uniform bed. It may, moreover, be caused to set complex machinery in motion, to turn millstones, throw shuttles, work saws and hammers, and drive piles. But every form of power here indicated would be derived from the original power expended in raising the water to the height from which it fell. There is no energy generated by the machinery; the work performed by the water in descending is merely the parcelling out and distribution of the work expended in raising it. In precisely this sense is all the energy of plants and animals the parcelling out and distribution of a power originally exerted by the sun. In the case of the water, the source of the power consists in the forcible separation of a quantity of the liquid from the lowest level of the earth's surface and its elevation to a higher position, the power thus expended being returned by the water in its descent. In the case of vital phenomena, the source of power consists in the forcible separation of the

Thus we see that not a peculiar agent, called Life, but a peculiar mode of operation is required to produce the special results we call vital forces, and as Life is thus the mere correlate of Physical forces, so Mind is the correlate of

atoms of chemical compounds by the sun-of the carbon and hydrogen, for example, of the carbonic acid and water diffused throughout the atmosphere, from the oxygen with which they are combined. This separation is effected in the leaves of plants by solar energy. The constituents of the carbonic acid and water are there torn asunder in spite of their mutual attraction, the carbon and hydrogen are stored up in the wood, and the oxygen is set free in the air. When the wood is burned the oxygen recombines with the carbon, and the heat then given out is of the precise amount drawn from the sun to effect the previous "reduction" of the carbonic acid. The reunion of the carbon with the oxygen is similar to the reunion of our falling water with the earth from which it had been separated. We name the one action 'gravity' and the other chemical affinity'; but these different names must not mislead us regarding the qualitative identity of the two forces. They are both attraction, and, to the intellect, the falling of carbon atoms against oxygen atoms is not more difficult of conception than the falling of water to the earth.

"The building up of the vegetable then is effected by the sun through the reduction of chemical compounds. All the phenomena of animal life are more or less complicated reversals of these processes of reduction. We eat the vegetable, and we breathe the oxygen of the air, and in our bodies the oxygen which had been lifted from the carbon and hydrogen by the action of the sun again falls towards them, producing animal heat and developing animal forms. Through the most complicated phenomena of vitality this law runs:—the vegetable is produced by the lifting, the animal by the falling of a weight. But the question is not exhausted here. The water which we used in our first illustration produces all the motion displayed in its descent, but the form of the motion depends on the character of the machinery interposed in the path of the water. And thus the primary action of the sun's rays is qualified by the atoms and molecules among which their energy is distributed. Molecular forces determine the form which the solar energy will assume. In the one case this energy is so conditioned by its atomic machinery as to result in the formation of a cabbage; in another case it is so conditioned as to result in the formation of an oak. So also as