Page:The Scientific Monthly vol. 3.djvu/26

 20 THE SCIENTIFIC MONTHLY

fitness of water is maximal*^ both as a solvent in all the bodily fluids^ and as a vehicle for most of the other chemical compounds. Further, since water itself is a solvent that fails to react with many substances (with nearly all biological substances) it serves also as a factor of bio- chemical stability. Water and the carbon dioxide of the atmosphere are the common source of every one of the complicated organic com- pounds and also the common end products of the materials yielding energy to the body. Proteins are made from supplies containing nitrogen material in addition.

In relation to Newton's law of action^ reaction and interaction the most important property of water is its dielectric constant Although itself only to a slight degree dissociated into ions it is the bearer of dis- solved electrolytic substances and possesses a high power of electric con- ductivity, properties of great importance in the development of the electric energy of the molecules and atoms in ionization. Thus water is the very best medium of electric ionization in solution, and was probably essential to the mechanism of life from its very origin.**

Through all the electric changes of its contained solvents water itself remains very stable because the molecules of hydrogen and oxygen are not easily dissociated; their union in water contributes to the living organism a series of properties which are the prime conditions of all physiological and functional activity. The great surface tension of water as manifested in capillary action is of the highest importance to plant growth; it is also an important force acting within the formed colloids, the protoplasmic substance of life.

PRIMORDIAL ENVIRONMENT — THE ATMOSPHERE

It is significant that the simplest known living forms derive their "life elements'* partly from the earth, partly from the water, and partly from the atmosphere. This was not improbably true also of the earliest living forms.

One of the mooted questions concerning the primordial atmosphere*' is whether or no it contained free oxygen. The earliest forms of life were probably dependent on atmospheric oxygen, although certain exist- ing bacterial organisms, known as " anaerobic,*' are now capable of exist- ing without it.

The primordial atmosphere was heavily charged with water vapor (HjO) which has since been largely condensed by cooling. In the early period of the earth's history volcanoes*^ were also pouring into the atmos- phere much greater amounts of carbon dioxide (COj) than at the

M These notes npon water are chiefly from the very suggestive treatise ''The Fitness of the Environment," hj Henderson, Lawrence J., 1913. 4« Henderson, Lawrence J., 1913, p. 256. 40 Becker, George P., letter of October 15, 1915. 47 Henderson, Lawrence J., 1913, p. 134.

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