صور الصفحة
PDF
النشر الإلكتروني

small ponds and streams which occasionally go dry with great loss of life. Man prepares for the coming winter, but the earthquake, tidal wave or volcanic eruption finds him helpless. If the coal supply failed this year our civilization might easily perish. Realizing that at some period it will fail, our ingenuity may enable us to find some substitute. Tides, winds and sun rays will some day be valued sources of energy.

Against the minor changes of storm and frost man easily protects himself. Not so, however, the lower forms of life. Frost indeed simplifies man's problems by killing his insect pests. Winter in the colder regions destroys countless myriads of organisms. Some scheme of suspended animation as it were must be evolved if any are to survive. Nature is fertile in inventions. By means of roots, unaffected by freezing and seeds which lie on the ground and germinate the next year, she saves her plants. For the animals there are eggs to hatch the next year, larvæ to penetrate the earth, cocoons from which the new form comes, hibernation for bears, migration for birds, while every rotten log or hollow tree literally teems with dormant life.

"The animal lives in an environment which is constantly changing. Its spontaneous movements are constantly bringing it into different conditions. It tends to regulate its internal processes by selecting the point in the environment in which its internal processes are not disturbed." 35 The mollusca living in the tide lines must be small enough to find protection by creeping into crevices of the rocks unless, as is usually the case, they have a strong pedal sucker which enables them to remain fixed. The blood temperature of hibernating rodents 35 SHELFORD, V. E. o. c., p. 29.

falls to about 40°, sometimes nearly to 35°. A little oxygen reaches them, but so little is required that immersion of an hour in carbon dioxid will not kill them. They must be fat when they begin the long sleep and must waken gradually. It is thought that if their temperature falls too low they awaken automatically, and by movement and the inhalation of oxygen again raise their temperature. The differences in the behavior of frogs in hot and cold water is interesting. In the former they are extremely lively, and as the temperature drops they become sluggish and drowsy.

Animals show marked powers of readaptation - to avoid the use of the word reason which some feel is a prerogative of the human. Our common chimney swifts once nested in hollow trees or crevices in the rock, but they accept chimneys as satisfactory substitutes. The black-throated hunting and other ground-building birds will, if their nests are destroyed, frequently build late in the season in trees. Ducks and geese that are hunted become extremely wary, but will quickly discover and frequent in large numbers a lake where shooting is prohibited. In parts of Africa because of the constant hunting the buffalo feeds only at night.

Even the daily changes are significant. Sleep results apparently from a drugging of the system by the carbon dioxid and other elements produced by everyday activity, which are less rapidly eliminated. At night, therefore, the eliminating process goes on till a balance is again secured. Possibly some structures are due to those daily changes. There is reason to believe that the barring of the feathers of some birds is due to the low blood pressure and poor circulation at night.

An interesting rhythm is shown by the phosphorescent

organisms of the sea. "It might be supposed at first thought that these phosphorescent organisms are not observed to emit light during the day because of the pressure of sunlight, and that if taken into a dark room they would be found to phosphoresce just as brilliantly as at night. Such is, however, not the case, not a spark can be elicited from them even by vigorous shaking, so long as there is daylight in the outer world. But if one stands by and watches in the dark room, as twilight is falling outside, although the organisms have been exposed to light all day, one observes the little lamps light up and flash out one by one like coruscating diamonds in the darkness till the whole fish is studded with flashing and disappearing light, a glorious sight in the darkness and stillness. . . . Regularly every evening the lights come out, and as regularly every morning they are extinguished, although all the intervening time the tiny living creatures have been kept in darkness." 36

It should be noted that changes within the body may make a fixed environment act as a stimulus. Animals change in many ways when physical maturity is reached. Thus the queen ant remains quietly in the dark nest while young. On the advent of maturity she leaves the earth, flies toward the light and keeps away from the ground. When fertilized she again seeks the earth, burrows into it and starts a new colony.

The rhythm of nature can hardly fail to impress the observer. The revolution about the sun, the ebb and flow of the tides and the waves of light and sound illustrate rhythm in the purely material world. Birth, youth, maturity, old age and death, show the cycle of life. The alternating periods of rest and activity, the

36 MOORE, B. The Origin and Nature of Life, pp. 250-251.

pulsations of the heart and the inhalation and expiration of the breath display it in the activities of organisms. Whether such rhythm also characterizes human institutions must be considered elsewhere.

Against such changes as have come in western Asia even man is largely powerless unless he moves. He may invent new measures which enable him to survive, but more likely he starts his migrations. No wonder then that Huntington says: "Finally it appears that the changes of climate have caused corresponding changes, not only in the distribution of man, but in his occupations, habits and even character." 37

It is not a matter of accident that the weather is the common basis of conversation the world over. Each and every primitive man came into close, daily, personal contact with nature. From this contact he had to get all the goods of everyday life. He was exposed to wind and storm. He saw the sun rise and set, the glory of the moon and stars. Now the civilized man has multiplied the contacts with nature in a sense he has weakened the force of each. His contact becomes more and more at second hand insofar as the great fundamentals are concerned. Hence he often ignores or denies even the great guiding forces sketched in this chapter. Yet in the qualities of the elements of the earth and man's adjustment thereto is the basis and start of all man's vaunted achievements as well as the limits thereof.

SUGGESTIONS FOR READING

CHAMBERLIN, T. C. Origin of the Earth. 1915.
CONN, H. W. The Story of the Living Machine. 1912.
CRILE, G. W. Man, An Adaptive Mechanism. 1916.

37 HUNTINGTON, E. The Pulse of Asia, p. 359.

DEXTER, E. G. Weather Influences. 1904.

HANN, J. Handbook of Climatology. 1903.

HELLPACH, W. Geopsychischen Erscheinungen. 1911.
HENDERSON, L. J. The Fitness of the Environment. 1913.
The Pulse of Asia. 1907.

HUNTINGTON, E.

66

66

JONES, H. C. A

LANKESTER, E. R.
METCHNIKOFF, E.

The Climatic Factor (as Illustrated in Arid
America). 1914.

Civilization and Climate. 1915.
New Era in Chemistry. 1913.
The Kingdom of Man. 1907.
The Nature of Man. 1903.

MOORE, B. The Origin and Nature of Life. 1912.
SEMPER, K. Animal Life.

SEMPLE, E. T.

[ocr errors]

1881.

American History and Its Geographic Conditions.

1903.

Influence of Geographical Environment. 1911. WOODRUFF, C. W. The Effect of Tropical Light on White Men.

1905.

« السابقةمتابعة »