Microbe Hunters

by Paul De Kruif

  “What are these things. . . are they microbes. . . are they alive? They do not move. . . maybe the sick blood of these poor beasts just changes into these threads and rods,” Koch pondered. Other men of science, Davaine and Rayer in France, had seen these same things in the blood of dead sheep; and they had announced that these rods were bacilli, living germs, that they were undoubtedly the real cause of anthrax—but they hadn't proved it, and except for Pasteur, no one in Europe believed them. But Koch was not particularly interested in what anybody else thought about the threads and rods in the blood of dead sheep and cattle—the doubts and the laughter of doctors failed to disturb him, and the enthusiasms of Pasteur did not for one moment make him jump at conclusions. Luckily nobody anxious to develop young microbe hunters had ever heard of Koch, he was a lone wolf searcher—he was his own man, alone with the mysterious tangled threads in the blood of the dead beasts.

  “I do not see a way yet of finding out whether these little sticks and threads are alive,” he meditated, “but there are other things to learn about them. . . ” Then, curiously, he stopped studying diseased creatures and began fussing around with perfectly healthy ones. He went down to the slaughter houses and visited the string butchers and hobnobbed with the meat merchants of Wollstein, and got bits of blood from tens, dozens, fifties of healthy beasts that had been slaughtered for meat. He stole a little more time from his tooth-pullings and professional layings-on-of-hands. More and more Mrs. Koch worried at his not tending to his practice. He bent over his microscope, hours on end, watching the drops of healthy blood.

  “Those threads and rods are never found in the blood of any healthy animal,” Koch pondered, “—this is all very well, but it doesn't tell me whether they are bacilli, whether they are alive. . . it doesn't show me that they grow, breed, multiply. . .”

  But how to find this out? Consumptives—whom, alas, he could not help—babies choking with diphtheria, old ladies who imagined they were sick, all his cares of a good physician began to be shoved away into one corner of his head. How-to-prove-these-wee-sticks-are-alive, this question made him forget to sign his name to prescriptions, it made him a morose husband, it made him call the carpenter in to put up a partition in his doctor's office. And behind this wall Koch stayed more and more hours, with his microscope and drops of black blood of sheep mysteriously dead—and with a growing number of cages full of scampering white mice.

  “I haven't the money to buy sheep and cows for my experiments,” you can hear him muttering, while some impatient invalid shuffled her feet in the waiting room, “besides, cows would be a little inconvenient to have around my office—but maybe I can give anthrax to these mice. . . maybe in them I can prove that the sticks really grow. . .”

  So this foiled globe-trotter started on his strange explorations. To me Koch is a still more weird and uncanny microbe hunter than Leeuwenhoek, certainly he was just as much of a self-made scientist. Koch was poor, he had his nose on the grindstone of a medical practice, all the science he knew was what a common medical course had taught him—and from this, God knows, he had learned nothing whatever about the art of doing experiments; he had no apparatus but Emmy's birthday present, that beloved microscope—everything else he had to invent and fashion out of bits of wood and strings and sealing wax. Worst of all, when he came into the living room from his mice and microscope to tell Frau Koch about the new strange things he had discovered, this good lady wrinkled up her nose and told him:

  “But, Robert, you smell so!”

  Then he hit upon a sure way to give mice the fatal disease of anthrax. He hadn't a convenient syringe with which to shoot the poisonous blood into them, but after sundry cursings and the ruin of a number of perfectly good mice, he took slivers of wood, cleaned them carefully, heated them in an oven to kill any chance ordinary microbes that might be sticking to them. These slivers he dipped into drops of blood from sheep dead of anthrax, blood filled with the mysterious, motionless threads and rods, and then—heaven knows how he managed to hold his wiggling mouse—he made a little cut with a clean knife at the root of the tail of the mouse, and into this cut he delicately slid the blood-soaked splinter. He dropped this mouse into a separate cage and washed his hands and went off in a kind of conscientious wool-gathering way to see what was wrong with a sick baby. . . “Will that beast, that mouse die of anthrax. . . Your child will be able to go back to school next week, Frau Schmidt. . . I hope I didn't get any of that anthrax blood into that cut on my finger. . . ” Such was Koch's life.

  And next morning Koch came into his home-made laboratory—to find the mouse on its back, stiff, its formerly sleek fur standing on end and its whiteness of yesterday turned into a leaden blue, its legs sticking up in the air. He heated his knives, fastened the poor dead creature onto a board, dissected it, opened it down to its liver and lights, peered into every corner of its carcass. “Yes, this looks like the inside of an anthrax sheep. . . see the spleen, how big, how black it is. . . it almost fills the creature's body. . . ” Swiftly he cut with a clean heated knife into this swollen spleen and put a drop of the blackish ooze from it before his lens. . .

  At last he muttered: “They're here, these sticks and threads. . . they are swarming in the body of this mouse, exactly as they were in the drop of dead sheep's blood that I dipped the little sliver in yesterday.” Delighted, Koch knew that he had caused in the mouse, so cheap to buy, so easy to handle, the sickness of sheep and cows and men. Then for a month his life became a monotony of one dead mouse after another, as, day after day, he took a drop of the blood or the spleen of one dead beast, put it carefully on a clean splinter, and slid this sliver into a cut at the root of the tail of a new healthy mouse. Each time, next morning, Koch came into his laboratory to find the new animal had died, of anthrax, and each time in the blood of the dead beast his lens showed him myriads of those sticks and tangled threads—those motionless, twenty-five-thousandth-of-an-inch thick filaments that he could never discover in the blood of any healthy animal.

  “These threads must be alive,” Koch pondered, “the sliver that I put into the mouse has a drop of blood on it and that drop holds only a few hundred of those sticks—and these have grown into billions in the short twenty-four hours in which the beast became sick and died. . . But, confound it, I must see these rods grow—and I can't look inside a live mouse!”

  How shall I find a way to see the rods grow out into threads? This question pounded at him while he counted pulses and looked at his patients' tongues. In the evenings he hurried through supper and growled good-night to Mrs. Koch and shut himself up in his little room that smelled of mice and disinfectant, and tried to find ways to grow his threads outside a mouse's body. At this time Koch knew little or nothing about the yeast soups and flasks of Pasteur, and the experiments he fussed with had the crude originality of the first cave man trying to make fire.

  “I will try to make these threads multiply in something that is as near as possible like the stuff an animal's body is made of—it must be just like living stuff,” Koch muttered, and he put a wee pin-point piece of spleen from a dead mouse—spleen that was packed with the tangled threads, into a little drop of the watery liquid from the eye of an ox. “That ought to be good food for them,” he grumbled. “But maybe, too, the threads have got to have the temperature of a mouse's body to grow,” he said, and he built with his own hands a clumsy incubator, heated by an oil lamp. In this uncertain machine he deposited the two flat pieces of glass between which he had put the drop of liquid from the ox-eye. Then, in the middle of the night, after he had gone to bed, but not to sleep, he got up to turn the wick of his smoky incubator lamp down a little, and instead of going back to rest, again and again he slid the thin strips of glass with their imprisoned infinitely little sticks before his microscope. Sometimes he thought he could see them growing—but he could not be sure, because other microbes, swimming and cavorting ones, had an abominable way of getting in between these strips of glass, over-growing, choking out the
slender dangerous rods of anthrax.

  “I must grow my rods pure, absolutely pure, without any other microbes around,” he muttered. And he kept flounderingly trying ways to do this, and his perplexity pushed up huge wrinkles over the bridge of his nose, and built crow's-feet round his eyes. . .

  Then one day a perfectly easy, a foolishly simple way to watch his rods grow flashed into Koch's head. “I'll put them in a hanging-drop, where no other bugs can get in among them,” he muttered. On a flat, clear piece of glass, very thin, which he had heated thoroughly to destroy all chance microbes, Koch placed a drop of the watery fluid of an eye from a just-butchered healthy ox; into this drop he delicately inserted the wee-est fragment of spleen, fresh out of a mouse that had a moment before died miserably of anthrax. Over the drop he put a thick oblong piece of glass with a concave well scooped out of it so that the drop would not be touched. Around this well he had smeared some vaseline to make the thin glass stick to the thick one. Then, dextrously, he turned this simple apparatus upside down, and presto!—here was his hanging-drop, his ox-eye fluid with its rod-swarming spleen, imprisoned in the well—away from all other microbes.

  Koch did not know it, perhaps, but this—apart from that day when Leeuwenhoek first saw little animals in rain water—was a most important moment in microbe hunting, and in the fight of mankind against death.

  “Nothing can get into that drop—only the rods are there—now we'll see if they will grow,” whispered Koch as he slid his hanging-drop under the lens of his microscope; in a kind of stolid excitement he pulled up his chair and sat down to watch what would happen. In the gray circle of the field of his lens he could see only a few shreddy lumps of mouse spleen—they looked microscopically enormous—and here and there a very tiny rod floated among these shreds. He looked—fifty minutes out of each hour for two hours he looked, and nothing happened. But then a weird business began among the shreds of diseased spleen, an unearthly moving picture, a drama that made shivers shoot up and down his back.

  The little drifting rods had begun to grow! Here were two where one had been before. There was one slowly stretching itself out into a tangled endless thread, pushing its snaky way across the whole diameter of the field of the lens—in a couple of hours the dead small chunks of spleen were completely hidden by the myriads of rods, the masses of thread that were like a hopelessly tangled ball of colorless yarn, living yarn—silent murderous yarn.

  “Now I know that these rods are alive,” breathed Koch. “Now I see the way they grow into millions in my poor little mice—in the sheep, in the cows even. One of these rods, these bacilli—he is a billion times smaller than an ox—just one of them maybe gets into an ox, and he doesn't bear any grudge against the ox, he doesn't hate him, but he grows, this bacillus, into millions, everywhere through the big animal, swarming in his lungs and brain, choking his blood-vessels—it is terrible.”

  Time, his office and its dull duties, his waiting and complaining patients—all of these things became nonsense, seemed of no account, were unreal to Koch whose head was now full of nothing but dreadful pictures of the tangled skeins of the anthrax threads. Then each day of a nervous experiment that lasted eight days Koch repeated his miracle of making a million bacilli grow where only a few were before. He planted a wee bit of his rod-swarming hanging-drop into a fresh, pure drop of the watery fluid of an ox-eye and in every one of these new drops the few rods grew into myriads.

  “I have grown these bacilli for eight generations away from any animal, I have grown them pure, apart from any other microbe—there is no part of the dead mouse's spleen, no diseased tissue left in this eighth hanging-drop—only the children of the bacilli that killed the mouse are in it. . . Will these bacilli still grow in a mouse, or in a sheep, if I inject them—are these threads really the cause of anthrax?”

  Carefully Koch smeared a wee bit of his hanging-drop that swarmed with the microbes of the eighth generation—this drop was murky, even to his naked eye, with countless bacilli—he smeared a part of this drop on to a little splinter of wood. Then, with that guardian angel who cares for daring stumbling imprudent searchers of nature standing by him, Koch deftly slid this splinter under the skin of a healthy mouse.

  The next day Koch was bending near-sightedly over the body of this little creature pinned on his dissecting board; giddy with hope, he was carefully flaming his knives. . . Not three minutes later Koch is seated before his microscope, a bit of the dead creature's spleen between two thin bits of glass. “I've proved it,” he whispers, “here are the threads, the rods—those little bacilli from my hanging drop were just as murderous as the ones right out of the spleen of a dead sheep.”

  So it was that Koch found in this last mouse exactly the same kind of microbe that he had spied long before—having no idea it was alive—in the blood of the first dead cow he had peered at when his hands were fumbling and his microscope was new. It was precisely the same kind of bacillus that he had nursed so carefully, through long successions of mice, through I do not know how many hanging-drops.

  First of all searchers, of all men that ever lived, ahead of the prophet Pasteur who blazed the trail for him, Koch had really made sure that one certain kind of microbe causes one definite kind of disease, that miserably small bacilli may be the assassins of formidable animals. He had angled for these impossibly tiny fish, and spied on them without knowing anything at all of their habits, their lurking places, of how hardy they might be or how vicious, of how easy it might be for them to leap upon him from the perfect ambush their invisibility gave them.

  3

  Cool and stolid, Koch, now that he had come through these perils, never thought himself a hero; he did not even think of publishing his experiments! To-day it would be inconceivable for a man to do such magnificent work and discover such momentous secrets, and keep his mouth shut about it.

  But Koch plugged on, and it is doubtful whether this hesitating, entirely modest genius of a German country doctor realized the beauty or the importance of his lonely experiments.

  He plugged on. He must know more! He went pell-mell at the inoculating of guinea-pigs and rabbits, and at last even sheep, with the innocent looking but fatal fluid from the hanging-drops; and in each one of these beasts, in the sheep just as quickly and horribly as the mouse, the few thousands of microbes on the splinter multiplied into billions in the animals, in a few hours they teemed poisonously in what had been robust tissues, choking the little veins and arteries with their myriads, turning to a sinister black the red blood—so killing the sheep, the guinea-pigs, and the rabbits.

  At one fantastic jump Koch had soared out of the vast anonymous rank and file of pill-rollers and landed among the most original of the searchers, and the more ingeniously he hunted microbes, the more miserably he tended to the important duties of his practice. Babies in far-off farms howled, but he did not come; peasants, with jumping aches in their teeth, waited sullen hours for him—and at last he had to turn over part of his practice to another doctor. Mrs. Koch saw little of him and worried and wished he would not go on his calls smelling of germicides and of his menagerie of animals. But so far as he was concerned his suffering patients and his wife might have been inhabitants of the other side of the moon—for a new mysterious question was worrying at his head, tugging at him, keeping him awake:

  How, in nature, do these little weak anthrax bacilli that fade away and die so easily on my slides, how do they get from sick animals to healthy ones?

  There were superstitions among the farmers and horse doctors of Europe about this disease, strange beliefs in regard to the mysterious power of this plague that hung always over their flocks and herds like some cruel invisible sword. Why, this disease is too terrible to be caused by such a wretched little creature as a twenty-thousandth-of-an-inch-long bacillus!

  “Your little germ may be what kills our herds, all right, Herr Doktor,” the cattle men told Koch, “but how is it that our cows or sheep can be all right in one pasture—perfectly hea
lthy, and then, when we take them into another field, with fine grazing in it, they die like flies?”

  Koch knew of this troublesome, mysterious fact too. He knew that in Auvergne in France there were green mountains, horrible mountains where no flock of sheep could go without being picked off, one by one, or in dozens and even hundreds by the black disease, anthrax. And in the country of the Beauce there were fertile fields where sheep grew fat—only to die of anthrax. The peasants shivered at night by their fires: “Our fields are cursed,” they whispered.

  These things bothered Koch—how could his tiny bacilli live over winter, even for years, in the fields and on the mountains? How could they, indeed, when he had smeared a little bacillus-swarming spleen from a dead mouse on a clean slip of glass, and watched the microbes grow dim, break up, and fade from view? And when he put the nourishing watery fluid of ox-eyes on these bits of glass, the bacilli would no longer grow; when he washed the dried blood off and injected it into mice—these little beasts continued to scamper gayly about in their cages. The microbes, which two days before could have killed a heavy cow, were dead!

  “What keeps them alive in the fields, then,” muttered Koch, “when they die on my clean glasses in two days?”