Kitabı oku: «Appletons' Popular Science Monthly, April 1899», sayfa 8
THE PHYSICAL GEOGRAPHY OF THE WEST INDIES
By F. L. OSWALD
I. – THE FAUNA OF THE ANTILLES: MAMMALS
The study of the geographical distribution of plants and animals has revealed facts almost as enigmatical as the origin of life itself. Water barriers, as broad as that of the Atlantic, have not prevented the spontaneous spread of some species, while others limit their habitat to narrowly circumscribed though not geographically isolated regions.
Tapirs are found both in the Amazon Valley and on the Malay Peninsula; the brook trout of southern New Zealand are identical with those of the Austrian Alps. Oaks and Ericacea (heather plants) cover northern Europe from the mouth of the Seine to the sources of the Ural; then suddenly cease, and are not found anywhere in the vast Siberian territories, with a north-to-south range rivaling that of all British North America.
But still more remarkable is the zoölogical contrast of such close-neighborhood countries as Africa and Madagascar, or Central America and the West Indian archipelago. The Madagascar virgin woods harbor no lions, leopards, hyenas, or baboons, but boast not less than thirty-five species of mammals unknown to the African continent, and twenty-six found nowhere else in the world.
Of a dozen different kinds of deer, abundant in North America as well as in Asia and Europe, not a single species has found its way to the West Indies. The fine mountain meadows of Hayti have originated no antelopes, no wild sheep or wild goats.
In the Cuban sierras, towering to a height of 8,300 feet, there are no hill foxes. There are caverns – subterranean labyrinths with countless ramifications, some of them – but no cave bears or badgers, no marmots or weasels even, nor one of the numerous weasel-like creatures clambering about the rock clefts of Mexico. The magnificent coast forests of the Antilles produce wild-growing nuts enough to freight a thousand schooners every year, but – almost incredible to say – the explorers of sixteen generations have failed to discover a single species of squirrels.
The Old-World tribes of our tree-climbing relatives are so totally different from those of the American tropics that Humboldt's traveling companion, Bonplant, renounced the theory of a unitary center of creation (or evolution), and maintained that South America must have made a separate though unsuccessful attempt to rise from lemurs to manlike apes and men. Of such as they are, Brazil alone has forty-eight species of monkeys, and Venezuela at least thirty. How shall we account for the fact that not one of the large West Indian islands betrays a vestige of an effort in the same direction?
More monkey-inviting forests than those of southern Hayti can not be found in the tropics, but not even a marmoset or squirrel-monkey accepted the invitation. In an infinite series of centuries not one pair of quadrumana availed itself of the chance to cross a sea gap, though at several points the mainland approaches western Cuba within less than two hundred miles – about half the distance that separates southern Asia from Borneo, where fourhanders of all sizes and colors compete for the products of the wilderness, and, according to Sir Philip Maitland, the "native women avoid the coast jungles for fear of meeting Mr. Darwin's grandfather."
The first Spanish explorers of the Antilles were, in fact, so amazed at the apparently complete absence of quadrupeds that their only explanation was a conjecture that the beasts of the forest must have been exterminated by order of some native potentate, perhaps the great Kubla Khan, whose possessions they supposed to extend eastward from Lake Aral to the Atlantic. The chronicle of Diego Columbus says positively that San Domingo and San Juan Bautista (Porto Rico) were void of mammals, but afterward modifies that statement by mentioning a species of rodent, the hutia, or bush rat, that annoyed the colonists of Fort Isabel, and caused them to make an appropriation for importing a cargo of cats.
Bush rats and moles were, up to the end of the sixteenth century, the only known indigenous quadrupeds of the entire West Indian archipelago, for the "Carib dogs," which Valverde saw in Jamaica, were believed to have been brought from the mainland by a horde of man-hunting savages.
But natural history has kept step with the advance of other sciences, and the list of undoubtedly aboriginal mammals on the four main islands of the Antilles is now known to comprise more than twenty species. That at least fifteen of them escaped the attention of the Spanish creoles is as strange as the fact that the Castilian cattle barons of Upper California did not suspect the existence of precious metals, though nearly the whole bonanza region of the San Joaquin Valley had been settled before the beginning of the seventeenth century. But the conquerors of the Philippines even overlooked a variety of elephants that roams the coast jungles of Mindanao.
Eight species of those West Indian incognito mammals, it is true, are creatures of a kind which the Spanish zoölogists of Valverde's time would probably have classed with birds – bats, namely, including the curious Vespertilio molossus, or mastiff bat, and several varieties of the owl-faced Chilonycteris, that takes wing in the gloom preceding a thunderstorm, as well as in the morning and evening twilight, and flits up and down the coast rivers with screams that can be heard as plainly as the screech of a paroquet. The Vespertilio scandens of eastern San Domingo has a peculiar habit of flitting from tree to tree, and clambering about in quest of insects, almost with the agility of a flying squirrel. There are times when the moonlit woods near Cape Rafael seem to be all alive with the restless little creatures; that keep up a clicking chirp, and every now and then gather in swarms to contest a tempting find, or to settle some probate court litigation. San Domingo also harbors one species of those prototypes of the harpies, the fruit-eating bats. It passes the daylight hours in hollow trees, but becomes nervous toward sunset and apt to betray its hiding place by an impatient twitter – probably a collocution of angry comments on the length of time between meals. The moment the twilight deepens into gloom the chatterers flop out to fall on the next mango orchard and eat away like mortgage brokers. They do not get fat – champion gluttons rarely do – but attain a weight of six ounces, and the Haytian darkey would get even with them after a manner of their own if their prerogatives were not protected by the intensity of their musky odor. The above-mentioned hutia rat appears to have immigrated from some part of the world where the shortness of the summer justified the accumulation of large reserve stores of food, and under the influence of a hereditary hoarding instinct it now passes its existence constructing and filling a series of subterranean granaries. Besides, the females build nurseries, and all these burrows are connected by tunnels that enable their constructors to pass the rainy season under shelter. They gather nuts, belotas (a sort of sweet acorns), and all kinds of cereals, and with their penchant for appropriating roundish wooden objects on general principles would probably give a Connecticut nutmeg peddler the benefit of the doubt.
They also pilfer raisins, and a colony of such tithe collectors is a formidable nuisance, for the hutia is a giant of its tribe, and attains a length of sixteen inches, exclusive of the tail. It is found in Cuba, Hayti, Jamaica, Porto Rico, Antigua, Trinidad, the Isle of Pines, Martinique, and two or three of the southern Bahama Islands, and there may have been a time when it had the archipelago all to itself. The Lucayans had a tradition that their ancestors found it on their arrival from the mainland, and in some coast regions of eastern Cuba it may still be seen basking in the sunlight —
"Sole sitting on the shore of old romance,"
and wondering if there are any larger mammals on this planet.
Its next West Indian congener is the Jamaica rice rat, and there are at least ten species of mice, all clearly distinct from any Old-World rodent, though it is barely possible that some of them may have stolen a ride on Spanish trading vessels from Central America.
Water-moles burrow in the banks of several Cuban rivers, and two genera of aquatic mammals have solved the problem of survival: the bayou porpoise and the manatee, both known to the creoles of the early colonial era, and vaguely even to the first discoverers, since Columbus himself alludes to a "sort of mermaids (sirenas) that half rose from the water and scanned the boat's crew with curious eyes."
Naturally the manatee is, indeed, by no means a timid creature, but bitter experience has changed its habits since the time when the down-town sportsmen of Santiago used to start in sailboats for the outer estuary and return before night with a week's supply of manatee meat. The best remaining hunting grounds are the reed shallows of Samana Bay (San Domingo) and the deltas of the Hayti swamp rivers. Old specimens are generally as wary as the Prybilof fur seal that dive out of sight at the first glimpse of a sail; still, their slit-eyed youngsters are taken alive often enough, to be kept as public pets in many town ponds, where they learn to come to a whistle and waddle ashore for a handful of cabbage leaves.
Fish otters have been caught in the lagoons of Puerto Principe (central Cuba) and near Cape Tiburon, on the south coast of San Domingo, the traveler Gerstaecker saw a kind of "bushy-tailed dormouse, too small to be called a squirrel."
But the last four hundred years have enlarged the list of indigenous mammals in more than one sense, and the Chevalier de Saint-Méry should not have been criticised for describing the bush dog of Hayti as a "canis Hispaniolanus." Imported dogs enacted a declaration of independence several centuries before the revolt of the Haytian slaves, and their descendants have become as thoroughly West Indian as the Franks have become French. A continued process of elimination has made the survivors climate-proof and self-supporting, and above all they have ceased to vary; Nature has accepted their modified type as wholly adapted to the exigencies of their present habitat. And if it is true that all runaway animals revert in some degree to the characteristics of their primeval relatives, the ancestor of the domestic dog would appear to have been a bush-tailed, brindle-skinned, and black-muzzled brute, intermittently gregarious, and combining the burrowing propensity of the fox with the co-operative hunting penchant of the wolf.
Fourteen years of bushwhacker warfare have almost wholly exterminated the half-wild cattle of the Cuban sierras, but the bush dog has come to stay. The yelping of its whelps can be heard in thousands of jungle woods and mountain ravines, both of Cuba and Hayti, and no variety of thoroughbreds will venture to follow these renegades into the penetralia of their strongholds. Sergeant Esterman, who shared the potluck of a Cuban insurgent camp in the capacity of a gunsmith, estimates the wild-dog population of the province of Santiago alone at half a million, and predicts that in years to come their raids will almost preclude the possibility of profitable cattle-breeding in eastern Cuba.
Still, the perro pelon, or "tramp dog," as the creoles call the wolfish cur, is perhaps a lesser evil, where its activity has tended to check the over-increase of another assisted immigrant. Three hundred years ago West Indian sportsmen began to import several breeds of Spanish rabbits, and with results not always foreseen by the agricultural neighbors of the experimenters. Rabbit meat, at first a luxury, soon became an incumbrance of the provision markets, and finally unsalable at any price. Every family with a dog or a trap-setting boy could have rabbit stew for dinner six times a week, and load their peddlers with bundles of rabbit skins.
The burrowing coneys threatened to undermine the agricultural basis of support, when it was learned that the planters of the Fort Isabel district (Hayti) had checked the evil by forcing their dogs to live on raw coney meat. The inexpensiveness of the expedient recommended its general adoption, and the rapidly multiplying quadrupeds soon found that "there were others." The Spanish hounds, too, could astonish the census reporter where their progeny was permitted to survive, and truck farmers ceased to complain.
In stress of circumstances the persecuted rodents then took refuge in the highlands, where they can still be seen scampering about the grassy dells in all directions, and the curs of the coast plain turned their attention to hutia venison and the eggs of the chaparral pheasant and other gallinaceous birds. On the seacoast they also have learned to catch turtles and subdivide them, regardless of antivivisection laws. How they can get a business opening through the armor of the larger varieties seems a puzzle, but the canis rutilus of the Sunda Islands overcomes even the dog-resisting ability of the giant tortoise, and in Sumatra the bleaching skeletons of the victims have often been mistaken for the mementos of a savage battle.
Near Bocanso in southeastern Cuba the woods are alive with capuchin monkeys, that seem to have escaped from the wreck of some South American trading vessel and found the climate so congenial that they proceeded to make themselves at home, like the ring-tailed colonists of Fort Sable, in the Florida Everglades. The food supply may not be quite as abundant as in the equatorial birthland of their species, but that disadvantage is probably more than offset by the absence of tree-climbing carnivora.
Millions of runaway hogs roam the coast swamps of all the larger Antilles, and continue to multiply like our American pension claimants. The hunters of those jungle woods, indeed, must often smile to remember the complaint of the early settlers that the pleasure of the chase in the West Indian wilderness was modified by the scarcity of four-footed game, and in the total number (as distinct from the number of species) of wild or half-wild mammals Cuba and Hayti have begun to rival the island of Java.
[To be continued.]
IRON IN THE LIVING BODY
By M. A. DASTRE
Iron occurs, in small and almost infinitesimal proportions, in numerous organic structures, in which its presence may usually be detected by the high color it imparts; and in the animal tissues is an important ingredient, though far from being a large one. It is essential, however, that the animal tissues, and particularly the liquids that circulate through them, should be of nearly even weight, else the equilibrium of the body would be too easily disturbed, and disaster arising therefrom would be always imminent. Hence the iron is always found combined and associated with a large accompaniment of other lighter elements which, reducing or neutralizing its superior specific gravity, hold it up and keep it afloat. Thus the molecule of the red matter of the blood contains, for each atom of iron, 712 atoms of carbon, 1,130 of hydrogen, 214 of nitrogen, 245 of oxygen, and 2 of sulphur, or 2,303 atoms in all. Existing in compounds of so complex composition, iron can be present only in very small proportions to the whole. Though an essential element, there is comparatively but little of it. The whole body of man does not contain more than one part in twenty thousand of it. The blood contains only five ten-thousandths; and an organ is rich in it if, like the liver, it contains one and a half ten-thousandths. When, then, we seek to represent to ourselves the changes undergone by organic iron, we shall have to modify materially the ideas we have formed respecting the largeness and the littleness of units of measure and as to the meaning of the words abundant and rare. We must get rid of the notion that a thousandth or even a ten-thousandth is a proportion that may be neglected. The humble ten-thousandth, which is usually supposed not to be of much consequence, becomes here a matter of value. Chemists working with iron in its ordinary compounds may consider that they are doing fairly well if they do not lose sight of more than a thousandth of it; but such looseness would be fatal in a biological investigation, where accuracy is necessary down to the infinitesimal fraction. The balances of the biologists must weigh the thousandth of a milligramme, as their microscopes measure the thousandth of a millimetre.
The great part performed by iron in organisms, what we may call its biological function, appertains to the chemical property it possesses of favoring combustion, of being an agent for promoting the oxidation of organic matters.
The chemistry of living bodies differs from that of the laboratory in a feature that is peculiar to it – that instead of performing its reactions directly it uses special agents. It employs intermediaries which, while they are not entirely unknown to mineral chemistry, yet rarely intervene in it. If it is desired, for example, to add a molecule of water to starch to form sugar, the chemist would do it by heating the starch with acidulated water. The organism, which is performing this process all the time, or after every meal, does it in a different way, without special heating and without the acid. A soluble ferment, a diastase or enzyme, serves as the oxidizing agent to produce the same result. Looking at the beginning and the end, the two operations are the same. The special agent gives up none of its substance. It withdraws after having accomplished its work, and not a trace of it is left. Here, in the mechanism of the action of these soluble ferments, resides the mystery, still complete, of vital chemistry. It may be conceived that these agents, which leave none of their substance behind their operations, which suffer no loss, do not have to be represented in considerable quantities, however great the need of them may be. They only require time to do their work. The most remarkable characteristic of the soluble ferments lies, in fact, here, in the magnitude of the action as contrasted with infinitesimal proportion of the agent, and the necessity of having time for the accomplishment of the operation.
Iron behaves in precisely the same way in the combustion of organic substances. These substances are incapable at ordinary temperatures of fixing oxygen directly, and will not burn till they are raised to a high temperature; but in the presence of iron they are capable of burning without extreme heat, and undergo slow combustion. And as iron gives up none of its substance in the operation, and acts, as a simple intermediary, only to draw oxygen from the inexhaustible atmosphere and present it to the organic substance, we see that it need not be abundant to perform its office, provided it have time enough. This action resembles that of the soluble ferments in that there is no mystery about it, and its innermost mechanism is perfectly known.
Iron readily combines with oxygen – too readily, we might say, if we regarded only the uses we make of it. It exists as an oxide in Nature; and the metallurgy of it has no other object than to revivify burned iron, remove the oxygen from it, and extract the metal. Of the two oxides of iron, the ferrous, or lower one, is an energetic base, readily combining with even the weakest acids, and forming with them ferrous or protosalts. Ferric oxide, on the other hand, is a feeble base, which combines only slowly with even strong acids to form ferric salts or persalts, and not at all with weak acids like carbonic acid and those of the tissues of living beings. It is these last, more highly oxidized ferric compounds that provide organic substances with the oxygen that consumes them, when, as a result of the operation, they themselves return to the ferrous state.
Facts of this sort are too nearly universal not to have been observed very long ago, but they were not fully understood till about the middle of this century. The chemists of the time – Liebig, Dumas, and especially Schönbein, Wöhler, Stenhouse, and many others – established the fact that ferric oxide provokes at ordinary temperatures a rapid action of combustion on a large number of substances: grass, sawdust, peat, charcoal, humus, arable land, and animal matter. A very common example is the destruction of linen by rust spots; the substance of the fiber is slowly burned up by the oxygen yielded by the oxide. About the same time, Claude Bernard inquired whether the process took place within the tissues, in contact with living matter in the same way as we have just seen it did with dead matter – the remains of organisms that had long since submitted to the action of physical laws – and received an affirmative answer. Injecting a ferric salt into the jugular vein of an animal, he found it excreted, deprived of a part of its oxygen, as a ferrous salt.
This slow combustion of organic matter, living or dead, accomplished in the cold by iron, represents only one of the aspects of its biological function. A counterpart to it is necessary in order to complete the picture. It is easy to perceive that the phenomenon would have no bearing or consequence if it was limited to this first action. With the small provision of oxygen in the iron salt used up, and, if reduced to the minimum of oxidation, the source of oxygen being exhausted, the combustion of organic matter would stop. The oxidation obtained would be insignificant, while the oxidation should be indefinite and unlimited, and it is really so.
There is a counterpart. The iron salt, which has gone back to the minimum of oxidation and become a ferrous salt, can not remain long in that state in contact with the air and with other sources of the gas to which it is exposed. It has always been known that ferrous compounds absorb oxygen from the air and pass into the ferric state; we might say that we have seen it done, for the transformation is accompanied by a characteristic change of color, by a transition from the pale green tint of ferrous bases to the ochery or red color of ferric compounds.
We can understand now what should happen when the ferruginous compound is placed in contact alternately with organic matter and oxygen. In the former phase the iron will yield oxygen to the organic matter; in the second phase it will take again from the atmosphere the combustible which it has lost, and will be again where it started. The same series of operations may be continued a second time and a third time, and indefinitely, as long as the alternations of contact with organic matter and exposure to atmospheric oxygen are kept up, the iron simply performing the part of a broker. The same result will occur if atmospheric air and organic matter are constantly together; the consumption will continue indefinitely, and the iron will perform the part of an intermediary till one of the elements of the process is exhausted.
This explanation was necessary to make clear the solution of the mystery of slow or cool combustion, the existence of which has been known since Lavoisier, without its mechanism being understood. That illustrious student gave out the theory that animal heat and the energy developed by vital action originated in the chemical reactions of the organism, and that, on the other hand, the reactions that produce heat consisted of simple combustions, slow combustions, that differed only in intensity from that of the burning torch. The development of chemistry has shown that this figure was too much simplified from the reality, and that most of these phenomena, while they are in the end equivalent to a combustion, differ greatly from it in mechanism and mode of execution. By this we do not mean to say that all the combustions are of this character, and that there do not exist in the organism a large number of such as Lavoisier understood, and of such as the combustions effected by the intervention of iron furnish the type of. Lavoisier's successors, Liebig among them, tried to find reactions conformed to this type. Their attempts were unsuccessful, but they had the happy result of revealing, if not the real function of iron in the blood, at least that of the red matter in which it is fixed.
The question of the presence of iron in the coloring matter of the blood gave rise to long discussions. Vauquelin denied it. He made the mistake of looking for iron in the form of a known compound, in direct combination with the blood, while later researches have shown that it is found almost exclusively in the red matter that tinges the globules, in a complicated combination that escapes the ordinary tests; or, according to a usual method of expression, it is dissimulated. Liebig also failed to find this combination, and it was not till 1864 that Hoppe-Seyler succeeded in obtaining it pure and crystallized. But Liebig had already perceived its essential properties, and was able to point out approximately its functions as early as 1845; yet the single fact that there was no assimilation possible between this substance and the salts of iron, cut this question off into a kind of negative suspense. Different from these compounds, it could not behave like them, and accomplish slow combustions of the same type. It is a remarkable fact, and one that illustrates well how iron preserves through all its vicissitudes some trace of its fundamental property of favoring the action of oxygen on substances, that this composition, so special and so different from the salts of iron, behaves nearly as they do. While it is not of itself an energetic combustible, it is, according to Liebig's expression, "a transporter of oxygen" – a luminous view, which the future was destined to confirm. Although the transportation is not produced by the mechanism supposed by Liebig, but by another, the general result is very much the same from the point of view of the physiology of the blood. The coloring matter of the blood conveyed by the globules fixes oxygen in contact with the pulmonary air, and distributes it as it passes through the capillaries upon the tissues. The globule of blood brings nothing else and distributes nothing else, contrary to the opinion that had been held before. The theory of slow combustion effected through iron, while not absolutely contradicted in principle, was not entirely confirmed in detail, so far as concerned iron, or the more prominently ferruginous tissue.
No search was made for other tissues or organs presenting more favorable conditions, for no others were known that had iron in themselves. The liver and the spleen were supposed to receive it from the blood under the complicated form in which it exists there, or under some equivalent form. It was not, therefore, supposed till within a very few years that the two conditions were realized in any organ that were required to secure a slow combustion by iron – that is, combinations resembling ferrous and ferric salts with a weak acid and a source of oxygen. The doubt has been resolved by recent studies. The liver fulfils the requirement. It contains iron existing under forms precisely comparable to the ferrous and ferric compounds, and is washed by the blood which carries oxygen in a state of simple solution in its plasma and of loose combination in its globules. Thus all the conditions necessary for the production of slow combustion are gathered here, and we can not doubt that it takes place. A new function is therefore assigned to the liver, and it becomes one of the great furnaces of the organism.
Compounds of iron are so abundant in the ground and the water that we need not be surprised when we find them in various parts of plants, and particularly in the green parts. Their habitual presence does not, however, authorize the conclusion that this metal is necessary to the support and development of vegetable life. Some substances, evidently indifferent, foreign, and even injurious, if they exist abundantly in a soil, may be drawn into roots through the movement of the sap, and fix themselves in various organs. This occurs with copper in certain exceptional circumstances when the soil is saturated with its compounds, and if such a condition should be found to be repeated over a large extent of country, we might be led, by analysis alone of its vegetable productions, to the false conclusion that copper was an essential or even necessary constituent of them. But the value of the part performed by an element can not be determined by analysis alone. Direct proofs are necessary for that, methodical and comparative experiments in cultivation in mediums artificially deprived or furnished with the element the importance of which we wish to estimate. This has been done for combinations of iron, and the utility of that metal, especially to the higher plants, has been made thereby to appear.
If iron is absent from the nutritive medium the plant will wither. If we sprout seeds in a solution from which this metal has been carefully excluded, the development will follow its regular course as long as the plant is in the condition properly called that of germination, or while it does not have to draw anything from the soil. The stem rises and the first leaves are formed as usual. But all these parts will continue pale, and the green matter, the granulation of chlorophyll, will not appear. Now, if we add a small quantity of salt of iron to the ground in which the roots are planted, or a much-diluted solution is sprinkled on the leaves and the stem, the chlorotic plant will recover its health and take on its normal coloration. Experiments of this sort make well manifest that iron is necessary to green plants, and they show, besides, the bearing of its action, and that what is most special and most characteristic in the phenomena of vegetable life may be traced exactly to the organization of that green matter. It was long thought that if iron was necessary for the formation of chlorophyll, it was because it had a part in its constitution. We know now that this is not so. The metal does nothing but accompany the chlorophyll in the granulation in which it is found.
