Chapter XIII · THE SENSE OF SMELL

In physics we hear of nothing nowadays but the Röntgen rays, which penetrate dense bodies and photograph the invisible for us. A fine discovery, but how insignificant in face of the surprises which the future reserves for us when, better-informed of the why and wherefore of things, we supplement with art the feebleness of our senses and succeed in rivalling, be it ever so little, the keenness of perception revealed by the brute creation.

How enviable, in many cases, is this animal superiority! It teaches us the poverty of our attainments; it declares the mediocrity of our sensory apparatus; it gives us evidence of impressions foreign to our nature; it proclaims realities so far in excess of our attributes that they astound us.

The man who has never seen a Dog hunting for truffles does not know one of the finest achievements of the sense of smell. Absorbed in its functions, the animal trots along, with its nose to the wind, at a moderate pace. It stops, questions the ground with its nostrils, scratches for a few seconds, without undue excitement, and looks up at its master:

“Here we are,” it seems to say, “here we are! On my word of honour as a Dog, there’s a truffle here.”

And it speaks the truth. The master digs at the point indicated. If the trowel goes astray, the Dog shows the man how to put it right by sniffing at the bottom of the hole. Do not be afraid of the stones and roots in between: despite the depth and intervening obstacles, the tuber will come. A Dog’s nose cannot lie.

“Subtlety of smell,” you say.

I have no objection, if by that you mean that the animal’s nasal passages are the organ of perception; but is the thing perceived always a mere smell, in the ordinary acceptation of the word, an effluvium such as our own senses understand it? I have some reason to doubt this. Let us set the matter forth.

I have had the good fortune on several occasions to accompany a Dog who was a great expert at his trade. Certainly he was nothing to look at, this artist whom I was so anxious to see at work: just a Dog, placid and deliberate in his ways, ugly, unkempt; the sort of Dog that you would never admit to your fireside. Talent and poverty often go hand in hand.

It was agreed between us that the Dog should act as he pleased and receive a bit of bread as his reward after each discovery, indiscriminately. Every spot scratched up by his paws was to be dug and the object indicated extracted without our troubling about its commercial value. In no case was the master’s experience to intervene and divert the dog from a spot where practice told him that nothing saleable was to be found, for, in drawing up my botanical lists, I preferred wretched and unmarketable products to the choicest morsels, though these of course were welcomed when they appeared.

Thus conducted, the underground botanizing was very fruitful. With his perspicacious nose, the Dog made me gather indifferently the large and the small, the fresh and the putrid, the scented and the unscented, the fragrant and the stinking. I was amazed at my collection, which comprised the greater part of the hypogean fungi in my neighbourhood.

What a variety of structure and above all of odour, the primary quality in this question of scent! There are some that have nothing more noticeable than a vague fungous mustiness, which is more or less evident in all. Some smell of turnips, of rotten cabbage; some are fetid enough to fill the collector’s house with their stench. The real truffle alone possesses the aroma dear to the epicure.

If smell, as we understand it, is the Dog’s only guide, how does he manage to find his way through all these incongruous odours? Is he apprised of the contents of the soil by a general emanation, the fungous effluvium common to the different species? In that case an extremely embarrassing question arises.

I paid some attention to the ordinary mushrooms, many of which, as yet invisible, announced their coming as imminent by cracking the surface of the ground. Now I never saw the Dog stop at any of those points where my eyes divined the cryptogam pushing back the earth with the thrust of its cap, points where the ordinary fungous smell was certainly most pronounced. He passed them by scornfully, with not a sniff, with not a stroke of his paw. And yet the thing was underground; and its reek was similar to others which he sometimes pointed out to us.

I came back from the Dog’s school with the conviction that the truffle-detecting nose has a better guide than smell, in the sense in which our olfactory powers realize it. It must perceive, in addition, effluvia of a different order, full of mystery to us, who are not equipped accordingly. Light has its dark rays, which are without effect upon our retinæ, but not apparently upon all. Why should not the domain of smell have its secret emanations, unknown to our senses but perceptible to a differently constructed organ of smell?

If the scent of the Dog leaves us perplexed to this extent, that it is impossible for us to say exactly or even to suspect what it perceives, it at least tells us plainly that we should be greatly mistaken to compare everything by human standards. The world of sensations is far larger than the limits of our sensibility admit. What a number of facts in the working of the forces of nature escape us for want of organs delicate enough to perceive them!

The unknown, that inexhaustible field which the future will cultivate, holds harvests in store for us beside which our present knowledge is but a pitiful gleaning. Under the sickle of science sheaves will one day fall whose grain to-day would seem a senseless paradox. Scientific illusions? Not so, if you please, but undeniable and positive realities, affirmed by the animal world, which in certain respects has a great advantage over the world of man.

In spite of his long professional practice, in spite of the aroma of the tuber which he is seeking, the rabassier cannot guess the presence of the truffle, which ripens in winter underground, at a depth of eighteen inches or so; he needs the aid of the Dog or the Pig, whose scent pries into the secrets of the soil. Well, these secrets are known to different insects even better than to our two helpers. In order to discover the tuber on which their family of grubs is to be fed, they possess a scent of exceptional perfection.

Long ago, from truffles dug up spoilt and teeming with vermin and placed in this condition in a glass jar with a layer of fresh sand, I obtained first a small red Beetle (Anisotoma cinnamomea, Panz.) and then various Diptera, including a Sapromyzon, who, with her sluggish flight and feeble frame, reminds me of a Fly, clad in yellow velvet, known as Scatophaga scybalaria, that placid frequenter of human excrement in autumn.

The latter finds her truffle on the surface of the ground, at the foot of a wall or hedge, man’s usual hasty refuge in the country; but how does the other know at what point underground lies hers, or rather her grubs’ truffle? To go down and hunt about in the depths is beyond her power. Her frail limbs, which the moving of a grain of sand would warp; her wings, which, if extended, would block her way through a gorge; her dress of stiff silk, militating against a smooth passage: these are all against her. The Sapromyzon is obliged to lay her eggs on the surface of the soil, but she must do so at the very spot beneath which the truffle lies, for the tiny grubs would die if they had to roam at random until they came upon their provender, which is always sparsely distributed.

The truffle-hunting Fly is therefore informed by her sense of smell of the spots favourable to her maternal plans; she possesses the scent of the rabassier Dog, indeed probably a better one, for she knows things by nature, having never been taught, whereas her rival has only received an artificial education.

It would be interesting to follow the Sapromyzon’s manœuvres, but the idea strikes me as impracticable. The insect is rare, flies away quickly and is soon out of sight. To observe it closely, to watch it at work would involve a great loss of time and a degree of assiduity of which I do not feel capable. Another discoverer of underground fungi shall reveal what the Fly could hardly be expected to show us.

Deceived by this armour, I at first took the insect for a member of the Dung-beetles’ corporation and brought it up as such in captivity. I served it with these stercoral dainties which are most appreciated by its presumed colleagues. But never, no, never did it consent to touch them. Fie, for shame! Dung to a Bolboceras! Well! What on earth did I take him for? The epicure expects something very different. He wants not exactly the truffle of our banquets, but its equivalent.

He is a robust fellow, who cares nothing for the winter. All through the cold season, whenever the weather turns a trifle milder, he leaves his house discreetly, at nightfall, and gathers, in the immediate neighbourhood of his burrow, a few Sheep-droppings, ancient, olive-shaped remains dried by the summer sun. He heaps them in a stack at the bottom of his larder, shuts the door and eats. When the provisions are all crumbed and drained of their niggardly juices, he climbs back to the surface and renews his stores. Thus does he spend the winter, never resting from his work, except when the weather is too severe.

The second object of my observations in the pine-wood is the Bolboceras. His burrows, distributed here and there, among those of the Minotaur, are easily distinguished. The Phalangist’s are surmounted by a bulky mound the materials of which are heaped into a cylinder as long as one’s finger. Each of these rolls is a load of rubbish pushed outside by the digger, thrusting with his back from below. The orifice moreover is closed whenever the Beetle is at home, either enlarging the shaft or peacefully enjoying his possessions.

The Bolboceras’ lodging is open and surrounded merely by a padding of sand. Its depth is slight, nine inches, hardly more. It goes straight down in very loose soil. It is easily inspected, therefore, if we take care first to dig a trench in front of it, which will enable us later to cut away the perpendicular wall, slice by slice, with the blade of a knife. The burrow then appears at full length, from top to bottom, in a semicylindrical shape.

Often the violated dwelling-house is empty. The insect has left during the night, having finished its business there and gone to settle elsewhere. The Bolboceras is a nomad, a night-walker, who leaves his home without regret and easily acquires a new one. Sometimes also the insect is found at the bottom of the pit: at one time a male, at another a female, but never the two at a time. The sexes, both equally zealous in digging burrows, work separately, not together. This is not, in fact, a family residence, containing the nursery of the young; it is a temporary abode, dug by each occupant for his own comfort.

Sometimes we find nothing there but the well-sinker, surprised during his work of excavation; sometimes, lastly—and the case is not uncommon—the hermit of the crypt embraces with his legs a small hypogean fungus, either intact or partly consumed. He clutches it convulsively, refuses to be parted from it. It is his booty, his fortune, his worldly goods. Scattered crumbs tell us that we have caught him feasting.

Let us take his prize away from him. We shall see a sort of irregular, rugged purse, closed on every side and varying in size between a pea and a cherry. Outside it is reddish, rough with little warts; inside it is smooth and white. The spores, which are ovoid and diaphanous, are contained, in rows of eight, in long satchels. By these characteristics we recognize an underground cryptogamous product, nearly related to the truffles and known to botanists as Hydnocystis arenaria, Tul.

This throws a light upon the habits of the Bolboceras and upon the reason why his burrows are so frequently renewed. In the calm of the twilight, the little gadabout takes to the fields, chirruping softly as he goes, cheering himself with song. He explores the soil, questions it as to its contents, just as the Dog does when hunting for truffles. His sense of smell warns him when the coveted morsel is underneath, covered by a few inches of sand. Certain of the exact spot where the thing lies, he digs straight down and never fails to reach it. As long as the provisions last, he does not go out again. Blissfully he feeds at the bottom of the well, heedless of the door left open or hardly barred.

When no more food remains, he moves, looking for another loaf, which will become the excuse for a fresh burrow, to be abandoned in its turn. Each fungus consumed represents a new house, which is a mere refectory, a traveller’s refreshment-room. Thus are the autumn and spring, the seasons of the hydnocystis, spent in the pleasures of the table, from one home to the next.

To study the rabassier insect more closely, in my own house, I should need a little store of its favourite fare. It would be waste of time to seek for it myself, by digging at random: the little cryptogam is not so plentiful that I can hope to strike it with my trowel without a guide. The truffle-hunter needs his Dog; my informer shall be the Bolboceras himself. Behold me turned into a rabassier of a new kind. I reveal my secret, which can only raise a smile from my original instructor in underground botany, if he should ever hear of my singular form of competition.

The subterranean fungi occur only at certain points, often in groups. Now the Beetle has been this way; with his delicate scent he has recognized the site as good, for the burrows are numerous hereabouts. We will therefore dig near the holes. The clue is accurate. In a few hours, thanks to the tracks left by the Bolboceras, I possess a handful of hydnocystes. It is the first time that I have gathered this particular fungus. Let us now catch the insect. That presents no difficulties: we have only to dig up the burrows.

At first there is nothing to see save the inevitable uneasiness due to the incidents of their exhumation, transport and confinement in an unknown place. My exiles from home try to escape, climb up the wire, burrow right at the edge of the enclosure. Night falls and things grow calmer. Two hours later, I come to take a last look at them. Three are still buried under a thin layer of sand. The five others have each dug a perpendicular shaft at the very foot of the straws which tell me where the fungi lie. Next morning, the sixth straw has its well like the others.

This is the moment to see what is happening underground. I remove the sand methodically in vertical slices. At the bottom of each burrow is a Bolboceras eating his truffle, the hydnocystis.

Let us repeat the experiment with the partly-consumed victuals. The result is the same. At one brief, nocturnal spell of work, the dainty is discovered underground and reached by means of a gallery which runs plumb to the spot where the morsel lies. There is no hesitation, no trial excavation guided by guesswork. This is proved by the surface of the soil, which everywhere is just as I left it when I smoothed it down. The insect could not have made straighter for the coveted object had it been guided by sight; it always digs at the foot of the straws, my sign-posts. The Dog, nosing the ground for truffles, hardly achieves this degree of precision.

Both of them search the subsoil very closely, at the level of the ground; and the object which they seek is not far down. Were they farther away, neither the Dog nor the insect would notice effluvia so subtle, not even the smell of a truffle. To make an impression at a great distance, powerful odours are needed, capable of perception by our olfactory sense. Then the exploiters of the odorous thing come hastening up on all sides from afar.

They have been informed by their sense of smell, at a great distance all around, whereas I myself can avoid the stench by taking a few steps back. Compared with their scent, mine is contemptible; but still, in their case as well as mine, there is really here what our language calls a smell.

I can do better still with the flower of the dragon arum (Arum dracunculus), so remarkable for its shape and for its unequalled stench. Imagine a wide, lanceolate blade, of a clarety purple, half a yard long and rolled below into an ovoid pouch the size of a hen’s egg. Through the opening of this wallet rises a central column springing from the bottom, a long, bright-green club, encircled at its base by two bracelets, one of ovaries, the other of stamens. Such, briefly described, is the flower, or rather the inflorescence, of the dragon arum.

For two days it exhales a frightful stench of carrion, worse than the proximity of a dead Dog would yield. During the hottest part of the day, with a wind blowing, it is loathsome, unbearable. Let us brave the infected atmosphere and go up to it; we shall behold a curious sight.

Informed by the foul odour, which spreads far and wide, various insects come flying along, such insects as make sausage-meat of small corpses—Toads, Adders, Lizards, Hedgehogs, Moles, Field-mice—which the husbandman hits with his spade and flings away disembowelled on the foot-path. They swoop down upon the great leaf, which, with its livid purple, looks like a strip of meat gone bad; they caper about, intoxicated by the smell of corpse which they love; they roll down the slope and are swallowed up in the purse. After a few hours of bright sunshine, the receptacle is full.

Let us look inside, through the narrow opening. No elsewhere could you see such a crowd. It is a mad whirl of backs and bellies, of wing-cases and legs, swarming, rolling over and over, amid the snap of interlocked joints, rising and falling, floating and sinking, seething and bubbling without end. It is a drunken revel, an epidemic of delirium tremens.

Some, few as yet, emerging from the mass, climb to the opening by means of the central pole or the walls of the enclosure. Will they take wing and make their escape? Not they! Standing on the brink of the chasm, almost free, they drop back into the whirlpool, in a fresh bout of intoxication. The bait is irresistible. Not one of them will quit the assembly until the evening, or perhaps next morning, when the heady fumes have evaporated. Then the mass becomes disentangled; and the insects extricate themselves from one another’s embraces and slowly, as it were regretfully, leave the place and fly away. At the bottom of this devil’s purse remains a heap of dead and dying, of severed limbs and disjointed wing-cases, the inevitable result of the frenzied orgy. Soon, Wood-lice, Earwigs and Ants will arrive and devour the deceased.

What were they doing there? Were they the prisoners of the flower? Had it converted itself into a trap which allowed them to enter, but prevented them from escaping, by means of a fence of converging hairs? No, they were not prisoners; they had full liberty to go away, as is shown by the final exodus, which is effected without impediment. Deceived by a false odour, were they doing their best to instal their eggs, as they would have done under a corpse? Not that either. There is no trace of an attempt at egg-laying in the dragon’s purse. They came, enticed by the smell of a dead body, their supreme delight; they were drunk with corpse; and they spun round frantically in an undertakers’ carnival.

When the bacchanal dance is at its height, I try to count the number of the arrivals. I rip up the floral pouch and pour its contents into a flask. Absolutely tipsy though they be, many would escape during the census, which I wish to take accurately. A few drops of carbon bisulphide deprive the crowd of motion. The counting then shows that there were over four hundred. Such was the living billow which I saw surging just now in the dragon’s purse.

Another detail deserves attention just as much as this enormous figure; and that is the complete absence of a number of other genera which are as passionately fond of small corpses as are the Dermestes and Saprini. My charnel-houses of Moles never fail to be visited by the Silphæ and Necrophori: Silpha sinuata, Fabr.; S. rugosa, Lin.; S. obscura, Lin.; Necrophorus vestigator, Hersch. The reek of the dragon arum leaves them all indifferent. None of them is represented in the ten flowers which I examine.

Nor are any Diptera, those other devotees of corruption. Several Flies, some grey or bluey, others a metallic green, come up, it is true, settle on the edge of the flower and even find their way into the fetid wallet; but they are almost immediately undeceived and fly away. Only the Dermestes and Saprini stay behind. Why?

My friend Bull, as decent a Dog as ever lived, had this among many other eccentricities: if he found in the dust of the road the dried up corpse of a Mole flattened under the heels of the passers-by, mummified by the heat of the sun, he would revel in rolling himself over it from the tip of his nose to the end of his tail; he would rub himself in it over and over again, shaken with nervous spasms, turning first on one side, then on the other. It was his sachet of musk, his flask of eau-de-Cologne. When scented to his liking, he would get up, shake himself and trot off, pleased as Punch with his pomade. Let us not abuse him and, above all, let us not discuss the matter. There are tastes of all kinds in this world.

Why should not some of the insects that dote on the smell of the dead have similar habits? Dermestes and Saprini come to the dragon arum; all day long they swarm in throngs, although free to go away; many of them die in the riot of the orgy. It is no rich provender that keeps them, for the flower gives them nothing to eat; it is not a question of laying eggs, for they take good care not to settle their grubs in that famine-stricken spot. What are they doing here, the frenzied ones? Apparently intoxicating themselves with fetidness, just as Bull did on the carcass of a Mole.

And this intoxication of smell attracts them from every part around, from very far perhaps, one cannot tell. Even so the Necrophori, in quest of an establishment for their young, hasten from the fields to my putrefying Moles. Both are informed by a potent smell, which offends our nostrils sixty yards away, but which travels ahead and delights them at distances where our own power of scent ceases.

The hydnocystis, the Bolboceras’ treat, has none of these violent emanations, capable of being diffused through space; it is devoid of smell, at least to us. The insect that hunts for it does not come from a distance; it inhabits the very places where the cryptogam lies. However faint the effluvia of the underground morsel, the prying epicure, equipped for the purpose, has every facility for perceiving them: he operates close by, on the surface of the soil. The Dog’s case is the same: he goes along searching, with his nose to the ground. Then, too, the real truffle, the essential object of his quest, possesses a most pronounced odour.

But what are we to say of the Great Peacock and the Banded Monk, making their way to the female born in captivity? They hasten from the ends of the horizon. What do they perceive at that distance? Is it really an odour, as our physiology understands the word? I cannot bring myself to believe it.

The Dog smells the truffle by sniffing the earth, quite close to the tuber; he finds his master at great distances by consulting the scent of his footprints. But is he able to discover the truffle hundreds of yards away, miles away? Can he join his master in the complete absence of a trail? Certainly not. For all his fineness of scent, the Dog is incapable of such a feat, which is performed, however by the Moth, who is put off neither by distance nor by the lack of any traces out of doors of the female hatched on my table.

It is a recognized fact that smell, ordinary smell, the smell that affects our nostrils, consists of molecules emanating from the scented body. The odorous matter dissolves and is diffused throughout the air by communicating to the air its aroma, even as sugar dissolves and is diffused in water by communicating to the water its sweetness. Smell and taste touch each other at some points; in both cases there is a contact between the material particles that give the impression and the sensitive papillæ that receive it.

Nothing can be simpler or clearer than that the dragon arum elaborates an intensely strong essence with which the air is impregnated and infected all around. Thus the Dermestes and Saprini, those passionate lovers of carrion smells, are informed by molecular diffusion. In the same way, the putrid Toad gives out and disseminates the stinking atoms that are the Necrophorus’ delight.

But what is materially emitted by the female Bombyx or Great Peacock? Nothing, according to our sense of smell. And this nothing is supposed, when the males congregate, to saturate an immense circle, several miles in radius, with its molecules! What the horrible stench of the dragon arum is unable to do the absence of odour is believed to accomplish! However divisible matter may be, the mind refuses to accept such conclusions. It would be tantamount to reddening a lake with an atom of carmine, to filling immensity with nothing.

Another argument. When my study is saturated beforehand with pungent odours which ought to overcome and destroy the most delicate effluvia, the male Moths arrive without the least sign of embarrassment.

A loud noise kills the faint note and prevents it from being heard; a bright light eclipses a feeble gleam. These are waves of the same nature. But the roar of thunder cannot cause the least jet of light to pale; nor can the dazzling glory of the sun stifle the least sound. Being of different natures, light and sound do not influence each other.

The experiment with the lavender-oil, naphthaline and the rest would therefore seem to prove that odour proceeds from two sources. For emission substitute undulation; and the problem of the Great Peacock is explained. Without losing any of its substance, a luminous point shakes the ether with its vibrations and fills a circle of indefinite width with light. This must almost express the working of the mother Bombyx’ tell-tale discharge. It does not emit molecules: it vibrates; it sets in motion waves capable of spreading to distances incompatible with a real diffusion of matter.

In its entirety, smell would thus seem to have two domains: that of the particles dissolved in the air and that of the ethereal waves. The first alone is known to us. It belongs also to the insect. It is this which informs the Saprinus of the dragon arum’s fetidity and the Silpha and Necrophorus of the stench of the Mole.

The second, which is far superior in its range through space, escapes us altogether, because we lack the necessary sensory equipment. The Great Peacock and the Banded Monk know it at the time of the nuptial rejoicings. And many others must share it in various degrees, according to the exigencies of their mode of life.

Like light, odour has its X-rays. Should science one day, instructed by the insect, endow us with a radiograph of smells, this artificial nose will open out to us a world of marvels.