Chapter II: Preface (2)

It rests on three groups of facts—matters of observation, which are not theory or guess work at all—but admitted by every one and demonstrated every day. These are—(1) Living things, each in its kind, produce a far larger number of young than can possibly grow up to maturity, since the kind of food and the situation necessary to each kind are limited and already occupied. Only one oyster embryo out of every five million produced (the reader may refer to p. 137 on this subject) grows up through all the successive stages of youth to the adult state. The total number of a species of animal or plant on the whole area where it is found does not increase. Even in those which produce a small number of young, there is great destruction, and taking all the individuals into consideration, only a single pair of young arrive at maturity to replace their parents. There is no exception to the rule that every organic being naturally multiplies at so high a rate that, if not destroyed, the progeny of a single pair would soon cover the earth. The elephant is reckoned the slowest breeder of known animals; it commences to breed at 30 years of age, dies at 100, and has six young in the interval. After 750 years, supposing all the offspring of a single pair fulfilled the rule and were not destroyed in an untimely way, there would be nearly nineteen million elephants alive descended from the first pair. There is then no doubt as to the enormous excess in the production of young living things, nor as to their necessary competition with one another of the most severe and inexorable kind; nor again as to the necessary death, in many species, of hundreds and thousands, for every one which survives to maturity and in its turn breeds.

(2) The second great fact is that among all the young born to a pair of parents, no two are exactly alike, nor are any exactly like their parents; nor are any two taken from all produced by all parents of that species exactly alike. They all resemble their parents at the corresponding age, in a general way and even very closely; but the resemblance is far from amounting to identity. This is called “variation.” It is familiar to us all in the case of the organism which we know best, and observe most closely, namely, man. It is also a matter of common observation in the case of dogs, cats, horses, and other domesticated animals. Many of these “variations” are exhibited in points of size, proportion, and colour, which are easily noted at once by the eye. But “variation” is really a deep-seated thing, and depends on causes which lie below the surface. We know that the offspring of men and of animals and of plants, give evidence of variations in what we call constitution, tendency, temperament, aptitude, strength, and that the colour, and even size of this or that part, are really only indications of a deep-seated difference in the living chemistry, the forces of nutrition and growth which reside in the living substance. The fact that many thousands of a species may be born and only a few survive, means therefore that many thousand varieties, often varieties not readily measured by the eye, are produced in each generation, from which a few individuals are in some way “selected” for survival.

(3) The third great fact is that though there is variation, amongst all the offspring in each generation, there is also a continual and definite inheritance by offspring of the qualities and structure of their parents to a degree which altogether preponderates over the variations. To put it in another way, we all know that every parental organism transmits to its young not only the qualities and structure of the species, or of the race, or of the family, but also transmits its own peculiarities or variations in which it departed from its parents, and from its brothers and sisters. This is best illustrated by our daily experience of human families.

These facts being admitted, and abundantly illustrated and traced in detail by years of observation and experimental breeding in all kinds of living things by hundreds of careful observers who have published the records of their studies, we come to the step where Darwin makes use of supposition or hypothesis. The question is, “Does the one which, out of the thousands of slightly different varieties, survives—do so by haphazard? or is there a necessarily acting state of things which selects that one special variety for survival?” Gardeners and breeders of pigeons, dogs, and cattle deliberately select the variations which they desire, breed from them, and so carry on by inheritance the special variation—whilst they ruthlessly destroy or restrain from breeding the numerous other variations in their “stock” which they do not desire. “If,” said Darwin, “there is any necessarily selective mechanism in Nature which could act as the breeder does, new varieties might be ‘naturally’ selected, and changes of form and appearance naturally established, which in the course of long ages would amount to such marked differences as separate what we call one species from another.” He showed that there is a natural mechanism of the required kind. “Since,” he says, “the competition among the members of any one kind or species for a place in life is so very severe, and the hostile circumstances so varied, and since all the competing offspring differ by ‘variation’ ever so little from one another, those varieties which are better suited in even the smallest degree to hold their own not merely in fighting with the others, but in withstanding injurious influences, in escaping enemies, and in procuring food, will be the ones which will survive, when a large number of cases, many thousands, extending over a large area and many years, are considered. Those which are ‘best fitted’ to get through the exceedingly numerous dangers and difficulties of life will be the survivors.” Hence we get the survival of the fit—the fit variations—by natural selection in the struggle for life. This, it will be observed, is an inference, and not a direct observation.

So long as the conditions remain practically or effectively unchanged, the animal or plant already “fitted” to them will be succeeded by those of its offspring which most resemble it in the essential points of “fitness.” But we know that in the course of ages, more or less rapidly, climates change, land emerges from the sea, islands join continents, continents become scattered islands, animals and plants migrate into regions previously uninhabited by them. As such changes gradually come on, the natural selection of favoured varieties will necessarily lead to the survival of others than those previously favoured, other variations better suited to the new conditions will survive.

The natural selection of favoured variations would not amount to much, were the variations not perpetuated by transmission to the young which they produce. This, it is common knowledge [see (3)], does take place. It is known also that a variation so established is as a result of the regular process of variation presented in larger volume or emphasised in character in some individuals of subsequent generations, and by continued “natural selection” it may become more and more a prominent or dominant feature of the race.

So far, the only assumption made by Mr. Darwin is that any or some of the endless variations which occur in all the offspring of wild plants and animals, in various combinations and degree in each individual, can be sufficiently important to determine the survival or non-survival of the organisms possessing them. That is a matter which has been largely studied and discussed. The verdict of those who have studied on the spot (as Darwin himself did) the teeming life of the tropics, the insects, birds, and plants of those regions, is that we are justified in considering that small variations are sufficiently important to turn the scale in favour of survival or non-survival. It is not easy for a man who is not a determined naturalist, constantly observing the ways of wild living things, to appreciate the evidence as to the efficacy of small variations, even were I able here to submit it to him. It is to be found in the published works of an army of investigators. In any case it is granted that effective variations—whether small or great—occur in nature, and that natural selection favours and perpetuates the new and fitter variety to the exclusion of the less fit.

The real difficulty to most people comes in the supposition next made by Mr. Darwin—namely, that this slow process of change by natural selection of favoured variations and their transmission and perpetuation by inheritance is sufficient to effect by its continued operation through enormous ages of time the conversion of a race of ancestral three-toed zebras into the one-toed horse of to-day; before that, of five-toed beasts into three-toed; at an earlier stage of fishlike creatures into four-footed land animals, and so on. You have to picture the whole series of animals and of plants which are now or ever have been, as two gigantic family trees or pedigrees, meeting in common ancestors of the simplest grade of microscopic life. All the diverging branches and twigs of these great “family trees” have been determined by the adaptation of living form to the endlessly varied conditions of life on this planet, by the natural selection or survival of variations and the transmission and accumulation of those variations from parent to offspring. This is a tremendous demand on the imagination. It is, however, not a difficult one to concede, when one is acquainted with the facts and conclusions of geology. The history of the crust of the earth was explained twenty years before the date of Darwin’s theory by Charles Lyell as due to the continued action through immense periods of time of the same natural forces which are now at work. And, moreover, the examination of the successive stratified deposits of the earth’s crust has yielded the remains of whole series of animals and of plants (simpler in character the older and deeper the rock in which they occur), which can be satisfactorily explained and interpreted as the ancestral forms from which present organisms have been developed.

The theory of the natural selection of variations as the moving spring in the gradual development of living forms from simplest living matter is Darwin’s theory. It is not possible to find any naturalist of consideration who does not accept it. There are various views held and discussed as to the cause of variation, as to the importance of small and of big variations, as to the non-transmissibility of some kinds of variation, and as to various peculiarities in regard to inheritance. They do not for the most part touch the main features of Mr. Darwin’s theory. No doubt we are learning and shall learn more about the facts of variation and the details of the process of hereditary transmission, but such increase of knowledge has not tended to undermine Mr. Darwin’s theory, and does not seem at all likely to do so.

On the occasion of the celebration at Cambridge in 1909 of the centenary of Darwin’s birth, I was invited by the Vice-Chancellor, on behalf of the University, to deliver in the Senate-house an address, others being given by representatives of the United States (Prof. Osborne), of Germany (Prof. Hertwig), and of Russia (Prof. Metchnikoff). The following is the text of that address:—

“I feel it a great honour to be called upon to speak here to-day, and to stand, on behalf of the naturalists of the British Empire, by the side of the distinguished men whose orations you have just heard.

“I think that the one thing about Charles Darwin which the large majority of British naturalists would wish to be to-day proclaimed, in the first place—with no doubtful or qualifying phrase—is that, in their judgment, after these fifty years of examination and testing, his ‘theory of the origin of species by means of natural selection or the preservation of favoured races in the struggle for life’ remains whole and sound and convincing, in spite of every attempt to upset it.

“I am not stating more than the simple truth when I say that, in the judgment of those who are best acquainted with living things in their actual living surroundings, ‘natural selection’ retains the position which Mr. Darwin claimed for it of being the main means of the modification of organic forms.

“Our admiration for the vast series of beautiful observations and interesting inquiries carried out by Darwin during his long life must not lead us to forget that they were devised by him in order to test the truth of his theory and to meet objections to it, and that they were triumphantly successful. They, together with the work of Alfred Russel Wallace and many of their followers, have more and more firmly established Darwin’s theory. On the other hand, no attempt to amend that theory in any essential particular has been successful.

“The nature of organic variation and of the character of the variations upon which natural selection can and does act was not, as we are sometimes asked to believe, neglected or misapprehended by Darwin. The notion that these variations are large and sudden was considered by him, and for reasons set forth by him at considerable length rejected. That notion has in recent years been resuscitated, but its truth has not been rendered probable by evidence either of such an accurate character or of such pertinence as would justify the rejection of Darwin’s fundamental conception of the importance of minute and ubiquitous variations.

“Further, in regard to the important facts of heredity connected with the cross-breeding of cultivated varieties, especially in regard to the blending or non-blending of their characters in their offspring and as to prepotency, it seems to me important that we should now and here call to mind the full and careful consideration given to this subject by Darwin. We cannot doubt that he would have been deeply interested in the numerical and statistical results associated with the name of Mendel. Those results tend to throw light on the mechanisms concerned in hereditary transmission, but it cannot be shown that they are opposed in any way to the truth of Darwin’s great theoretical structure—his doctrine of the origin of species.

“It has often been urged against Darwin that he did not explain the origin of variation, and especially that he has not shown how variations of sufficient moment to be selected for preservation in the struggle for existence have in the first place originated. The brief reply to the first objection is that variation is a common attribute of many natural substances of which living matter is only one. In regard to the second point, I desire to remind this assembly that Darwin described with special emphasis instances of what he calls ‘correlated variability.’ In my opinion he has thus furnished the key to the explanation of what are called useless specific characters and of incipient organs. That key consists in the fact that a general physiological property or character of utility is often selected and perpetuated, which carries with it distinct, even remote, correlated growths and peculiarities obvious to our eyes, yet having no functional value. At a later stage in the history of such a form these correlated growths may acquire value and become the subject of selection.

“It is thus, as it seems to me, and as, I believe, to the great body of my brother naturalists, that Darwin’s theory stands after fifty years of trial and application.

“The greatness of Charles Darwin’s work is, and will be for ever, one of the glories of the University of Cambridge. It is fitting on the present occasion that one who speaks on behalf of English men of science should call to mind the nature of his connection with this great University and the peculiarly English features of his life-story and of that fine character which endears his memory to all of us as much as his genius excites our admiration and reverence. Darwin was not, like so many a distinguished son of Cambridge, a scholar or a fellow of his college, nor a professor of the University. His connection with the University and the influence which it had upon his life belong to a tradition and a system which have survived longer in our old English universities than in those of other lands. Darwin entered the University, not seeking a special course of study with the view of professional training, nor aiming at success in competitive examinations for honours and emolument. He came to Cambridge intending to become a clergyman, but blessed with sufficient means and leisure to enable him to pursue his own devices, to collect beetles, to explore the fen country, and to cultivate his love of nature. It was thus that he became acquainted with that rare spirit Henslow, the Cambridge professor of botany, and it is through Henslow and the influence of his splendid abilities and high personal character upon Darwin that Cambridge acquired the right to claim the author of the ‘Origin of Species’ as a product of her beneficence and activity as a seat of learning.

“As an Oxford man and a member of Exeter College, I may remind this assembly that in precisely the same way Darwin’s dearest friend and elder brother in science, Charles Lyell, had a few years earlier entered at Exeter College, and by happy chance fallen under the influence of the enthusiastic Buckland, the University reader in geology and a Canon of Christ Church. The wise freedom of study permitted and provided for in those long-passed days by Oxford and Cambridge is what has given the right to claim the discovery, if not the making, of Lyell to the one and of Darwin to the other.

“Darwin’s love of living nature and of the country life are especially English characteristics; so, too, I venture to think, are the unflinching determination and simple courage—I may even say the audacity—with which he acquired, after he had left the University, the wide range of detailed knowledge in various branches of science which he found necessary in order to deal with the problem of the origin of the species of plants and animals, the investigation of which became his passion.

“The unselfish generosity and delicacy of feeling which marked Darwin’s relations with a younger naturalist, Alfred Russel Wallace, are known to all. I cannot let this occasion pass without citing those words of his which tell us most clearly what manner of man he was and add to his splendid achievements as an intellectual force—a light and a beauty of which every Englishman must be proud. When in old age he surveyed his life’s work he wrote:—‘I believe that I have acted rightly in steadily following and devoting my life to science.’

“To have desired to act ‘rightly,’ and to be able to think of success in life as measured by the fulfilment of that desire, is the indication and warrant of true greatness of character. We Englishmen have ever loved to recognise this noble kind of devotion in our national heroes.”

VI

METCHNIKOFF AND TOLSTOI

The Darwin celebration at Cambridge, in June 1909, brought a wonderful assemblage of celebrated biologists from all parts of the world to this country. There never has been seen such a company of great discoverers of all nationalities in the field of natural history and the science of living things, as were present in the University of Cambridge during that week. Even philosophers, moralists, and jurists were present to join with the one great political leader of our own country who really knows and appreciates the importance of the scientific study of Nature—the Right Hon. Arthur J. Balfour—in his fervent and heartfelt tribute to the influence of Darwin’s work and theory in all departments of human knowledge, thought, and activity. One of the most remarkable men present was Elie Metchnikoff. He represented both Russia, the country of his birth and earlier scientific work, and his adopted country, France, where, as sub-director of the Institut Pasteur, his later and most important researches have been carried on. Russia was also represented by Salensky, late director of the Museum of St. Petersburg, well known to us all as a discoverer in the embryology (growth from the egg) of marine animals, and by Timiriazeff, the botanist, renowned for his work on the mode in which leaf-green or “chlorophyll” enables green plants to obtain their food from the gases of the atmosphere. France had other representatives in Edmond Perrier, director of the Paris Museum, and Prince Roland Bonaparte.

Metchnikoff was one of the four representatives selected by the University to deliver orations in the Senate House in honour of Darwin. He especially drew attention to the influence of Darwin’s theory on the study of disease. The recognition of the derivation of man from animal ancestors, and of the complete community of the structure and the chemical activity of the organs of man with those of the organs of animals, had made (he said) the study of the diseases of animals a necessary feature in the understanding of the diseases of man. The far-reaching principle of Darwin that the mechanisms and processes observed in the bodies of plants and of animals (including man) must have been selected in the struggle for existence and perpetuated, because of their utility, led Metchnikoff to inquire what is the value or use of the process called inflammation and of the “eating corpuscles,” or “phagocytes” (so named by him), which wander from the blood into inflamed tissues. This question had led him to the discovery that the phagocytes engulf and destroy disease-germs, and are the great protectors of the animal and human body against bacteria and other germs which enter cut and wounded surfaces, and would start disease were there not “inflammation,” which is nothing more nor less than a nerve-regulated stagnation of the circulation of the blood at the wounded spot, and the consequent arrival at this spot of thousands of “phagocytes,” which pass out of the stagnant blood through the walls of the fine blood-vessels. These armies of phagocytes proceed to eat up and destroy all the germs which fall on to the wound—from the air, from dirty surfaces, and from the skin. The utility of inflammation and its gradual development, according to Darwinian principles, in the animal series, was shown twenty years ago by Metchnikoff. His important work on “immunity” and on infection and on protection against germ-caused disease is thus seen to be one of the many flourishing and valuable branches of knowledge which have originated from Darwin’s great conception and his example in experiment and inquiry.

Metchnikoff is now devoting all his attention to the possibility of prolonging human life. The facts seem to show that if we ate and drank only what is best for us, and led lives regulated by reason and knowledge, we should, nearly all, attain to 80 or even 100 years of age, having healthy minds and healthy bodies. We should die quietly and comfortably at the end, with much the same feeling of contentment in well-earned final repose as that which we now experience in going to sleep at the end of a long and happy day of healthy exercise and activity. Metchnikoff thinks that the causes of too early death may be ascertained, and when ascertained avoided or removed. In 1870, in a little book on _Comparative Longevity_, I distinguished what we may call the “possible life,” or “potential longevity,” of any given human being from his or her “expectation” of life. Potential longevity has been well called our “lease” of life. It is probably not very different in different races of men or individuals, and is probably higher than King David thought, being 100 to 120 years, and not merely 70 years. We all, or nearly all, fail to last out our “lease” owing to accidents, violence, and avoidable, as well as unavoidable, disease; so that 70 years is named as our tenure when the injury done to us by unhealthy modes of life and by actual disease are considered as inevitable. Metchnikoff proposes to discover and to avoid those conditions which “wear down” most of us and produce “senility” and “death” before we have really run out our lease of life.

Human beings die most abundantly in the earliest years of life. Statistics show that at birth the chance or expectation of life is only 45 years, whilst at 10 years old you may expect to live to be 61. At 30 you have not a much better chance—you will probably, if you are what is called a “healthy” life, die when you are 65. But if you survive to be 50 you may expect, if you have not any obvious disease or signs of “break up,” another twenty years, and will probably die at 70; surviving to 60, you may expect, if you are what passes for “healthy,” to live to 73. Now, it is especially with regard to life after 40 or 50 years of age that Metchnikoff is interested. Those who have survived the special dangers and difficulties of youth, and have arrived at this mature age, ought to be able to realise much more frequently than they do something like the full “lease of life.” There seems to be no reason why they should not avoid the usual rapid “senile changes” or weakness of old age, and survive, as a few actually do, to something like 100. The causes of “senile change” and the way to defeat their operation are what Metchnikoff is studying. Hardening of the walls of the arteries set up by certain avoidable diseases contracted in earlier life, and by the use of alcohol (not only to the degree which we call “drunkenness,” but to such a degree as to make one depend on it as a “pick-me-up”), is an undoubted cause of that weakness and liability to succumb to other diseases which is so general after 50 years of age. The causes which produce hardened arteries can be avoided. Another cause of senile changes is declared by Metchnikoff, to arise from the continual absorption of poisonous substances produced by the decomposition of partially digested food in the lower bowel or large intestine. This is at present the chief subject of his study. It is to prevent the formation of these poisons that he has introduced the use of sour milk, prepared with the lactic ferment. Since the Cambridge celebration he has been in London in order to examine the condition of certain patients from whom a distinguished English surgeon has found it necessary to remove the “large intestine.” Metchnikoff wishes to ascertain what bacteria, poison-producing or other, are present in these patients, and what is their general chemical condition now that this poison-producing part of the digestive canal has been taken from them.

In Paris, Metchnikoff has some very interesting experiments in progress with bats. He uses the large tropical fruit-eating bats, or “flying foxes.” They have a very short intestine, and very few bacteria and of very few kinds are to be found in its contents. On the other hand, there are as many as thirty distinct kinds of bacteria producing putrefaction or other chemical change in the digestive canal of man—and their quantity is gigantic. They pervade the whole contents of the human digestive canal by millions. By properly feeding the flying foxes in his laboratory in Paris Metchnikoff has actually succeeded in getting rid of all bacteria from their digestive canal, so that he now has adult mammalian animals, not very remote from man in their structure, food, and internal chemistry, which are absolutely free from the intestinal parasitic bacteria which he supposes to cause poisoning and senile changes in man. It is obvious, without pursuing the matter into further detail here, that Metchnikoff is now in a position to test his views as to the action of particular kinds of bacteria—he has animals which are free from them. He can make an experiment, keeping some of his bats still free from bacteria and causing some to be largely infected by this or that kind, and he can compare the result in regard to the health and chemical condition of the animals. So, too, the patients from whom the lower intestine has been removed may very probably furnish him (through his assistant who remains in London) with important facts for comparison with the condition of persons who have not been deprived of this part of the digestive apparatus.

I have given this sketch of what my friend is doing in order to furnish some notion of the kind of investigation which he pursues. He does not expect to extend the “lease” of human life, but by ascertaining in a definite scientific way the true rules of internal and external “hygiene” he does hope to give mankind an increased “expectation” of life; in fact, to enable a vastly larger number of men and women to enjoy that lease to the full, and to die without disappointment and regret, even with contentment and pleasure, at the end of it.

Metchnikoff was in Russia in the spring of 1909, and spent a day with Tolstoi. They were “fêted” and photographed together, the greatest artist and the greatest scientist of Russia. Tolstoi is 81 years of age. He took Metchnikoff out alone for a drive in his pony-cart so as to talk with him without interruption. “What do you think of life?” was the first question he asked, and one which it took my friend some time to answer. In regard to vegetarianism the two great men did not agree. When Metchnikoff declared that there was less cruelty on man’s part in killing wild animals to eat them than in leaving them to die by the tooth and claw of predaceous animals or from starvation, Tolstoi observed that that was argument and reason, and that he paid no attention to them; he only guided himself (he said) by sentiment, which he felt sure told him what was good and right! He was, however, deeply interested in an account of the cannibalism of savage races of men, concerning which he seemed to be quite uninformed. He also was profoundly interested in Metchnikoff’s view that Goethe, in the second part of _Faust_, is chiefly bent upon depicting the persistence of the amorous passion in old age—of which Goethe himself was an example—and Tolstoi declared that this gave a new meaning to the poem, which he had always hitherto found dull and unintelligible. But when Metchnikoff described in glowing words the joy and even rapture with which man will hereafter welcome the repose and mystery of death, having completed a long and healthy life of some hundred years, Tolstoi declared that this was indeed a fine conception, although it was entirely subversive of his own notions as to the significance of life and death. Tolstoi also stated that he had written his stories rapidly and without effort, but that his essays on morality and religion had cost him great labour; and, further, that he could not now remember the former, though the latter still were developing and incessantly occupied his thought.

It was admitted with regret by Darwin that he ceased in middle age to care for poetry and art, though there seems to be no doubt that he mistook fatigue and preoccupation of mind for a real change in taste and power of appreciation. It is interesting to place beside this the case of the great literary artist, Tolstoi, who not only frankly confesses that he refuses to be guided by reason and follows sentiment, but is also profoundly ignorant upon all the most ordinary topics of human life outside his own village, and of all Nature and her workings. Would Tolstoi have been a greater or a smaller artist if he had had a larger knowledge of the things that are? Was Darwin’s great scientific achievement really related to an innate indifference to what is called “poetry”? I will not now discuss the matter, but I am convinced that so far as natural gift is concerned, the keenest scientific capacity is not only compatible with the fullest sensibility to art and with the power of poetical vision and expression, but is often accompanied by them; and, further, that the work of an artist, if he is a great artist, cannot be hampered by knowledge. It is only the small talent or the feeble genius that can be paralysed rather than developed by the fullest experience and the widest knowledge. Necessary incompatibility of mental qualities has no place in this matter; what has led to the erroneous assumption that it has, is the excessive exercise by exceptional individuals of certain powers—a specialism necessary for effort and success, but deliberately chosen, and not due to an inborn one-sidedness.

VII

THE LAND OF AZURE BLUE

The Côte d’Azur whither many of my readers will be travelling—in thought, if not in reality—about Easter time, is well named the Land of Azure Blue, for it is the blueness of the sea, of the sky, and of the distant rocks and mountains, as well as much of the vegetation, which is when the sun shines, its special charm. And although one has some wet and some cloudy days, yet the sun does shine there with a strength and brilliancy not to be enjoyed in the early part of the year on the Atlantic and North Sea coast. This tract of country, more commonly known to English people as the Riviera, has very special meteorological conditions owing to its position as the narrow strip of shore-line existing between the vast mass of the Western Alps and the Mediterranean Sea. It is warmed by the sea, and lies too close under the mountains to be caught by any winds from the north, and at many points is also effectively protected from both east and west winds by rocky spurs of the great mountain chain.

The Riviera is a constant source of delight to those who love flowers and beautiful vegetation of all kinds. But few of its visitors appreciate the fact that it is really from end to end one big garden, cultivated for ages by its inhabitants, and full of plants introduced by man which at present seem at first sight to be characteristic natives of it, but are, in reality, quite distinct from its primitive vegetation. This primitive vegetation is now represented only in what is locally called the “maquis”—what we should, perhaps, term the “scrub” or “bush” in English. It comprises some pines, the juniper, the lovely rock roses, balsams, rosemary, the giant heath (bruyère), from which our briar-root pipes are made, the larger thyme, the myrtle, the rose of Provence, two kinds of lavender, and many aromatic plants with grey hairy leaves, and often provided with sharp thorns as additional defences against browsing goats. The delicious perfumes of these hardy inhabitants of the dry, rocky grounds, where little or no grass can flourish, are developed by them as a protection against browsing animals, who cannot tolerate much of these pungent volatile oils, although mankind extracts them and uses them in the manufacture of such scents as eau-de-Cologne and also in cookery.

Many a visitor to the Riviera never strays from the cultivated fields and roadways into this scrub-land. The olive tree, which forms so prominent and beautiful a feature in the panorama of gardens which unrolls itself as we steam or drive along the coast from Toulon to Mentone and from Mentone to Genoa and Spezzia, is not a native plant; it was introduced in prehistoric times, and has been again and again re-established by emigrants from Italy; but it was brought to Italy from the East. It is astonishing how many of the cultivated trees of the Riviera have the same kind of history—the vine came from India in prehistoric times, the fig tree more recently from Persia, the lemon from India, the orange and the peach tree from China. All of them were introduced in very ancient times to the eastern parts of the Mediterranean basin, and so gradually were carried to the shores of the Ligurian sea, and would die out here were they not to a certain extent under the care of ownership.

The so-called “mimosa,” so abundant here, with its pretty, sweet-scented, yellow blossom, is an Australian acacia, only introduced some sixty years ago; whilst the eucalyptus—a most picturesque and effective addition to the landscape—is a still later introduction from Australia. The cypress, that darkest and most shapely of conifers, long lines of which proclaim to the traveller as he passes Avignon his arrival in the true “South,” is not a native of these parts, although it flourishes in suitable situations. It was introduced in mediæval times from the East. So, too, the palms, though some have been cultivated for centuries, have been largely imported from extra European localities in the last century. There is a native European palm. It is a kind of fan-palm, and grows here. I have gathered it in Sicily. It does not “rear its stately head” more than a foot from the ground, and is known to botanists as _Chamærops humilis_. The gigantic Mexican agave and the prickly-pear cactus were introduced in the seventeenth century from the New World, though, according to Sir Herbert Tree’s scenery, they were growing at Cape Miseno in the time of Antony and Cleopatra! Bamboos of many kinds have been introduced here from the Far East, and flourish exceedingly.

The orange tree was brought from India (whither it was carried from China) and established in Southern Europe in mediæval times, though known to the ancient Greeks and Romans. There are as many as 120 different varieties of the orange tree now cultivated on the shores of the Mediterranean, including, besides those which are valued for their sweet juicy pulp, those which furnish bergamot oil and similar aromatic products. The “issue pea” of old apothecaries, which was bound into a cut made in a patient’s flesh for the purpose of producing inflammation and suppuration, with the notion that such treatment was beneficial, was a minute unripe orange dried, and, no doubt, to some extent, antiseptic.

Besides the introduced trees, we find, in ground which has been more or less under cultivation, and not, therefore, of the nature of the “maquis,” or scrub-land, some beautiful plants, such as the narcissus, iris, and various lilies. One very small and graceful tulip is, I believe, regarded as native to the soil, but a magnificent crimson tulip, as large as the varieties cultivated in English gardens, which I have found abundantly in open park-like land under olive trees at Antibes, is said to have been introduced from Persia in the Middle Ages, and to have taken kindly to the Riviera. It is the _Tulipa oculus solis_. In the same locality were growing many brilliantly coloured “stellate” anemones.

There is, of course, a third group or “lot” of plants on the Riviera, which consists of those brought from all parts of the world during the past century, and regularly cultivated and cared for in gardens. The climate of the Riviera enables the gardener to grow all sorts of sub-tropical plants in the open air, and a long list of them could be given. The wonderfully brilliant crimson creeper, Bougainvillia, covers walls by the roadways, and even the railway stations, with its rich colour at this season. A delightful book by the distinguished botanist, Professor Strasburger, describing and picturing in colours many of the cultivated as well as the wild plants of the Riviera, has lately been published (in English) at a small price.

The animals which come under the notice of those who go in search of spring sunshine to the Riviera are far less numerous than the plants. But there is one which is dear to all, although it makes such a noise for an hour or so about sunset that some people are irritated or even alarmed by it. This is the little green tree-frog, Fig. 1, which now comes forth from its winter sleep, and assembles in thousands—guided by the “croak” or “call” which is produced by the males. The females have a very small voice comparatively. I kept two—a male and female—through a winter in London, and when the spring came the male terrified the household one night by unexpectedly uttering his cry—loud and sharp—to which the female replied. “Wharr! biz” is the nearest expression I can give in letters to the two sounds. After a great many evenings spent in these rhythmical declamations, the little frogs collect round pools and tanks, and at last drop from the trees into the water, and there deposit their spawn. When producing his cry the male distends the skin of his throat like a balloon. The air is driven alternately from it into the lungs and back again over the vocal chords, which vibrate with no uncertain sound. These little frogs are easy to keep in an inverted bell-jar or in a fern-case, but must be fed regularly with flies and spiders, which they catch by a sudden dab of the tongue at the moment of alighting from a long leap on to the glass where the insect is crawling. They can hold on to smooth glass or leaves by means of their sucker-like toes (Fig. 1).

The colour of the upper surface of the South European tree-frog is a most vivid and smoothly laid-on grass-green. Occasionally the colour becomes altered to a brownish purple, but returns after a day or two to its usual bright green tint. A great rarity is the blue variety of this frog—the enchanted Prince of the Côte d’Azur—blue as the sky and the sea around him—the true _genius loci_. I obtained one a few years ago at Mentone, and kept it alive for three years in London. Its blue was the blue of the forget-me-not or the finest turquoise. When it died (I believe of old age, and not from discomfort or disease) I examined its skin very carefully with the microscope, and compared it with that of the ordinary green tree-frog, in order to make out the cause of their difference in colour.

At Mentone there is a little shop where one may purchase green tree-frogs and ornamental cages in which to keep them. Every year the dealer has two or three specimens of the blue variety on sale—their backs and heads looking like bits of turquoise-blue kid. Visitors have sometimes wrongly supposed that the blue frogs had been artificially changed in colour, but they are real, natural varieties. A similar substitution of blue for green has been noticed as a rare variation in other kinds of frogs and toads in other countries. It really consists in a suppression of yellow pigment.

The interesting thing about the colour of the little tree-frogs is that we find, on careful examination of the skin of a dead specimen with the microscope, that there is no green nor yet any blue “pigment” present in it. I found, on examining the blue specimen which died after living three years with me, that there is only black pigment overlaid by a colourless, semi-transparent layer of skin. In this outer skin in the ordinary green specimens there is scattered a quantity of excessively minute yellow particles, which, mixed with the blue, produce the green appearance. The fact is, that the wonderful “dead” turquoise-blue of the blue frog is a colour-effect similar to that of the blue sky and the blue of the human eye. It is produced by a peculiar reflection of the light from minute colourless particles, without the assistance of any blue-coloured substance. The distinction of these two modes of producing blue colour is important.

Certain transparent bodies are so constituted that when a beam of light is directed so as to pass through them, the red, yellow, green, and purple rays which exist in colourless sunlight are stopped, and only the blue rays come through. Such a body is blue copperas, or sulphate of copper; another is methyl blue, one of the aniline dyes; another is pure water, which gives only a slight advantage to the blue rays, so that the light must pass through a thickness of 30 feet or more before the blue tint is obvious. Thus, part of the blueness of the Côte d’Azur is accounted for—namely, the blueness of the sea when the sunlight is strong and is reflected from the white rocks and sand lying 30 feet to 100 feet below the surface of the water.

There are, of course, other self-coloured transparent bodies which allow only rays of one colour to pass. Thus, blood-red, or hæmoglobin, the pigment of the blood, allows chiefly red rays to pass through it. Yellow rays only pass through a solution of saffron or of chromic acid; green only or chiefly through green copperas (sulphate of iron) or through leaf-green or chlorophyll. Colour is very generally due in natural objects to such transparent bodies which absorb or stop all the coloured rays of light as it passes through them, excepting those of one tint—or, to be more correct, nearly all except those of one tint.

But the blue of the blue frog and a great deal of the blue in nature is due to another cause. If you are a smoker, or the friend of a smoker, watch the fine curling lines of smoke ascending from a cigar when it is being consumed in bright sunshine. You will see that it has a blue, even an azure blue, tint as the sunlight falls upon it. But if you let the smoke get between the sun and your eyes you will notice that the little curling clouds are no longer blue, but reddish-brown, in appearance. The smoke is not a transparent blue; looked at as a transparent body, it is brown! Further, when the smoke has passed into the smoker’s mouth and is ejected after remaining there for a few seconds, the cloud no longer looks blue, even when the sunlight falls on it and is reflected from it to your eye. It is now opaque white or colourless, with, perhaps, a faint tinge of blue. This change is due—as was shown by the experiments of the late Professor Tyndall upon a variety of clouds and vapours—to the cooling of the smoke and the increased size of the floating particles which coalesce as the temperature falls. The larger particles reflect white light, and the cloud is no longer blue. A cloud formed by the finest particles gives the strongest blue to the light reflected from it, and it is to this property of the finest particles of water-cloud floating in our atmosphere that the blue colour of the sky is due.

No doubt the question arises, “Why do clouds of the finest particles reflect a predominant amount of blue light rather than yellow or green or red?” That question is answered by mathematicians in accordance with what is ascertained as to the nature and properties of light, but it would require a long treatise to put those matters even in outline before the reader. We may in the meanwhile accept the conclusions of the physicists, and interest ourselves in seeing how they apply to some of the concrete facts about colour in Nature.

There are other instances of “blueness” due to the reflection of light from a cloud of excessively minute particles besides that of the azure sky and the blue, curling smoke of a wood fire. A familiar instance is the blueness of translucent bodies, such as the “white” of a boiled plover’s egg, especially when a bit of it is placed on a dead-black ground. The bluish appearance of watered London milk is another instance. These bodies look blue owing to the fine, colourless particles suspended in them, which act on light in the same way as do the fine particles of newly-produced smoke. Another very interesting case is the blue colour of the iris of the eye of man and other animals. It is not due to any blue pigment, but to a reflection from fine particles in the translucent, but turbid, tissue of the iris overlying the dark, black chamber of the eye. White geese and white cats frequently have blue eyes, the blue being thus produced. The only pigment which occurs in the human eye is a brown one, which gives a colour varying from amber yellow to very dark brown, almost black, according to the quantity present. When a very little of it is present it gives, in combination with the blue appearance of the unpigmented iris, a green tint, so that green eyes owe their colour to the same combination of causes as does the green skin of the little tree-frogs, or “rainettes.”

No solvent will extract any pigment from the skin of the blue frog—nor by the finest trituration can one obtain any coloured particles from it; only fine black granules can be separated. Alcohol removes the yellow pigment from the skin of a green tree-frog (killed, of course, for the experiment), and for a minute or two the skin becomes blue when its yellow pigment is thus removed by immersion in spirit; but it rapidly becomes a dull greyish-brown in colour, and so remains; the green cannot be preserved in spirit-specimens. It is not fully explained how such a uniform “dead” blue is produced by the reflection of light from fine particles, as that observed in the blue frog’s skin.

It appears that the blue and the green colour in the feathers of birds is in most, if not all, cases produced in the same way as the blue and green of the tree-frog’s skin. It would be interesting were it found possible to produce a full dead-blue colour by experimentally placing a coat of a translucent but turbid colourless medium on a dead-black plate. This, however, has not been done as a deliberate experiment. It is, however, recorded that Goethe was delighted to find what he considered to be a confirmation of his theory of colour when a friend showed him an oil-painting of a gentleman in a black coat which when wetted with a sponge turned bright blue. The picture had been recently “restored,” and the varnish on the black coat was not “dry.” It was precipitated by the water from the sponge, mixing with the spirit which held it in solution. A fine colourless cloud was thus produced overlying the black paint of the coat, and, as in the case of the cerulean frog, a dead-blue colour, due to reflection of the light by the fine particles, was the result. Some friendly physicist might repeat this experiment and study the matter in detail. The red, orange, and yellow colours of birds’ feathers are produced by pigments which are either insoluble or only soluble with great difficulty in fluids of the nature of ether. There is, however, an exception in the case of the African birds called Turacous, or Plantain-eaters. These birds have some large quill-feathers in the wing of a rich crimson colour. This splendid red pigment can be washed out of the feathers by water which is slightly alkaline, and a fine blood-red solution is obtained. Why this curious exception exists we do not know. The extracted colour is found to contain the element copper as one of its chemical components. Plantain-eaters kept in cages have sometimes washed all the colour out of their feathers owing to the water supplied to them for bathing and drinking having become foul and ammoniacal, and thus capable of dissolving the red pigment.

The cultivation on the Riviera of flowers for sale as “cut flowers” in Paris, London, and Berlin, in the colder months of the year, is now an enormous business, bringing many thousands of pounds yearly to the small gardeners around Hyères, St. Raphael, Nice, and Mentone. Roses, violets, carnations, “mimosa” of various kinds, anemones, lilies, and narcissus are sent literally in tons by quick trains several times a week from these realms of sunshine to the dreary North. The commencement of this trade was due to the suggestion made some fifty years ago by Alphonse Karr, the French poet and journalist, who had a beautiful garden of his own at St. Raphael, and found that he could produce flowers in profusion through the winter. Two years ago I visited this garden (which now belongs to a French painter) at the beginning of April, and found it full of interesting flowers and shrubs, enormous bamboos, palm trees, some twenty different “mimosas,” eucalyptus of several species, camellia trees, and rose-bushes in quantity.