THE

QUARTERLY REVIEW

No. 477.-OCTOBER, 1923.

Art. 1.-THE NEW BIOLOGY.

1. Principles of General Physiology. By W. M. Bayliss. Longmans, 1915.

2. Le Mouvement Biologique en Europe. By Georges Bohn. Paris: Colin, 1921.

3. Tier und Pflanze in intrazellularer Symbiose. By P. Buchner. Berlin: Borntraeger, 1921.

4. Senescence and Rejuvenescence. By C. M. Child. Chicago, 1915.

5. Outlines of Evolutionary Biology. By A. Dendy. Third Edition. Constable, 1923.

6. On Growth and Form. By D'Arcy W. Thompson. Cambridge University Press, 1917.

And other works.

A

THERE are various ways in which a science or a department of science may become new. An important discovery may enforce reconsideration of a large range of facts, as in the case of radio-activity or of hormones. new idea may act as a ferment, like the idea of evolution in biology, or the idea of the conservation of energy in physics. Or the change may be due to a new contact, as when psychology joined hands with physiology. In other cases a transformation has followed the introduction of a new method or a new instrument, as may be well illustrated by the influence of spectroscopy on astronomy, or of microscopy on zoology.

But however a science becomes new, the change is organic, like growth or development. It is very rarely that there is anything like casting off a threadbare Vol. 240.-No. 477.

garment, or pulling down an edifice and beginning afresh. What happens is more like the re-invigoration of a developing organism. The old is not superseded or discarded, it is re-habilitated or subsumed in a new synthesis. The evolution theory did not depreciate the sound results of comparative anatomy, but it suffused them with light. The discovery of the regulative system of endocrine glands did not replace our conception of the integrative action of the nervous system. What it did was to give the concept of integration new life.

One of the central ideas in biology is that of the linkage of lives. It is an old idea, but it was Darwin who made it grip men's minds, for he had the vision of the web of life more vividly than any one before or since. It is characteristic of the new biology that it has set the idea of the correlation of organisms in the centre of its thinking. Nothing lives or dies to itself; everything, as John Locke said, is a retainer to some other part of Nature. Cats have to do with the clover crop in Britain and with the incidence of the plague in India; earthworms affect the wheat supply and water-wagtails the success of sheep-farming. Squirrels do not seem at first sight to have much connexion with the harvest fields, but when they are drastically shot down in the interests of forestry there is a multiplication of wood-pigeons, on whose squabs they levy useful toll, and a wood-pigeon may fill its crop with a thousand grains of oats in the course of a forenoon. The bees and the flowers are hand and glove; the thrush plants the mistletoe and the ants sow the seeds of the broom; the minnow nurses the freshwater mussel, and, by devouring larval mosquitoes, checks the spread of malaria.

Long nutritive chains bind organisms together in successive incarnations. The more sunshine in spring the greater is the multiplication of Diatoms and Peridinid Infusorians in the English Channel, and the more these animalcules increase the thicker in the sea-soup is the stock of small crustaceans (Copepods chiefly) on which the daintily-feeding mackerel very largely depend. To make a pound of cod requires ten pounds of whelks; to make a pound of whelks requires ten pounds of seaworms; to make a pound of sea-worms requires ten

pounds of organic sea-dust. And so the world goes

round!

One of the plants most inimical to man's interests is the bracken, for it destroys good pasture and it is so sturdy and insurgent that it can conquer even the heather. The encroachments may be met by laborious cutting and by spraying with sulphuric acid, but it would be more promising to discover new uses for the fern. It makes excellent bedding, it has strong antiseptic qualities, it contains a considerable quantity of potash, and so on. A few experiments have shown that the fish-yield of freshwater lochs can be greatly improved by pitching cartloads of cut bracken into the waters. Their slow decay promotes the multiplication of animalcules, on which small crustaceans and the like depend, and thus the fishes are fed. These experiments should be continued, for it may be that bracken cast upon the waters will return to us in many days in the form of trout.

Every one knows that widely separated forms of life are often linked together by being the two hosts of one parasite. Remembering that the sheep and the little water-snail are the two hosts of the liver-fluke, Dr Leiper was able during the War to prove that the very formidable human parasite called Bilharzia spends part of its juvenile life inside freshwater snails. From these the microscopic larvæ pass into the water and swim freely. If an opportunity offers they enter man through cracks and weak spots in the skin. Every third child of the 30,000 born annually in Cairo is infected with Bilharzia, and the parasite is a serious menace to adults as well. Dr Leiper not only traced the lifehistory of the worm, but also has saved thousands of lives by showing that the dangerous intruders can be kept back by good filters, and that the free-swimming stages die within thirty-six hours in water that is kept stagnant. The subtleties of parasitology are often almost incredible. There is a remarkable fluke called Leucochloridium that lives in the intestine of singing-birds on the continent. The microscopic eggs are voided on the meadow and may be eaten by a small snail (Succinea), in whose stomach they hatch. Each larva gives rise to a strange branched form, with ramifications which extend

up to the snail's horns, where they pulsate with great rapidity, sometimes twice a second. The swollen and agitated horns are all the more conspicuous because they have become banded with red and green pigment. They have been, so to speak, painted by the parasite. If a Blackcap or some similar perching songster is attracted by the snail on a leaf and pecks off the pulsating horn, the branch of the parasite, which is now full of larvæ of another generation, closes up automatically at its base, so that there is no loss of the multitudinous microscopic progeny. Now the investigators tell us that if the Blackcap swallows the horn then and there, nothing happens. The fluke-parasites are digested. But if the bird gives the tit-bit to its nestling, which has a weaker digestion, then infection occurs and the extraordinary life-cycle begins again.

The new biology has prepared us then for the linking together of lives apparently far out of touch with one another. The malarial parasites pass from man to man by aid of the mosquito; the Trypanosome microbe, that causes Sleeping Sickness, is disseminated by the tse-tse fly; bubonic plague is transferred from rat to man by the intermediation of the rat-flea. Some of the finest pearls appear to be formed in the pearl-oyster as the sepulchres of the minute parasitic larvæ of flukes and tapeworms.

If the idea of the web of life is Darwinian, as it distinctively is, then it cannot be called new. But the point is that it has now been recognised as a leading idea, as expressing a fundamental fact in the economy of Nature, with illustrations more abundant and farreaching than was previously supposed. Let us take a few modern instances. One of the most striking biological facts in many parts of Britain is the success of the heather. It grows exuberantly on mountain and moorland where few other flowering plants can make a living. There is soil, but it is unready; there is water, but it is apt to be physiologically unavailable. How does the heather flourish so well? The answer is that it is involved in a very intimate partnership with a fungus, which penetrates through and through the heather, from root to stem, into every leaf, even into the flower and its seed. What an individual could not

do, a firm achieves. The heather is a dual organism; it is like a flowering lichen! If it stood alone it would be a remarkable curiosity, but it is only an instance of a kind of partnership that is now known to be common, between the highest plants and the lowest. The list of flowering plants with fungi (mycorhiza) living in profitable partnership with their roots is already a long one. The root-tubercles of Leguminosa, due to nests of symbiotic Bacteria, are familiar, and of considerable importance in agriculture. Familiar, we say, but it does not seem at all clear as yet how it is that the partnership enables the quiet-living plant to capture the nitrogen of the air—a feat which man accomplishes by harnessing waterfalls to electric machines and sending terrific lightning discharges through the air.

Considerable progress has been made with the physiology of animal luminescence. Indeed the chemistry of the transformation of energy has outrun our knowledge of what the light means in the life of the creature. The gleams, so badly called 'phosphorescent,' may be lanterns, or lures, or danger-signals, or love-lights, or recognition-marks, or what-not. Speculation is rife because ecological observations and experiments have been few. As to the physiology, however, it seems to have been well-established in the case of the fire-fly, the crustacean Cypridina, and the rock-boring bivalve, the piddock or Pholas, that a ferment-like substance, luciferase, acts on an oxidisable substance, luciferin, changing chemical energy into radiant energy. But our present point, in connexion with the linkages of organisms, is illustrated by the evidence that in some cases, such as luminous cuttlefishes, the light is produced by nests of Bacteria. They are like those that we see in the dark on the glistening surface of the haddock hung up to dry; but they are living in regularised partnership with the animal. In some cases, therefore, the luminescent animal shines with a borrowed light.

Many beetles eat wood, but that is Spartan diet. It is not surprising, therefore, that some of the beetles which habitually bore in fresh wood have learned to grow a mould that yields what is called 'ambrosia.' The fungus lives on the wood and its sap, and spreads over the walls of the tunnels that the beetles make.