Microbe Hunters

by Paul De Kruif

  “What I have to do is to grow yeasts in a soup that has no albumen in it at all. If yeasts will turn sugar into alcohol in such a soup—then Liebig and his theories are finished.” Defiance was in every fiber of him. This business was turning from an affair of cold science into a purely personal matter. But it was one thing to have this bright idea and quite another to find an albumenless food for yeasts—yeasts were squeamish in their tastes, confound them—and he fussed around his drafty attic and was for weeks an exasperated, a very grumpy Pasteur. Until one morning a happy accident cleared the road for him.

  He had by chance put some salt of ammonia into an albumen soup in which he grew the yeasts for his experiments. “What's this,” he meditated. “The ammonia salt keeps disappearing as my yeasts bud and multiply. What does this mean?” He thought, he fumbled—“Wait! The yeasts use up the ammonia salt, they will grow without the albumen!” He slammed shut the door of his attic room, he must be alone while he worked—he loved to be alone as he worked just as he greatly enjoyed spouting his glorious results to worshipful, brilliant audiences. He took clean flasks and poured distilled water into them, and carefully weighed out pure sugar and slid it into this water, and then put in his ammonia salt—it was the tartrate of ammonia that he used. He reached for a bottle that swarmed with young budding yeasts; with care he fished out a yellowish flake of them and dropped it into his new albumenless soup. He put the bottle in his incubating oven. Would they grow?

  That night he turned over and over in his bed. He whispered his hopes and fears to Madame Pasteur—she couldn't advise him but she comforted him. She understood everything but couldn't explain away his worries. She was his perfect assistant. . .

  He was back in his attic next morning not knowing how he had got up the stairs, not remembering his breakfast—he might have floated from his bed directly to the rickety dusty incubator that held his flask—that fatal flask. He opened the bottle and put a tiny cloudy drop from it between two thin bits of glass and slid the specimen under the lens of his microscope—and knew the world was his.

  “Here they are,” he cried, “lovely budding growing young yeasts, hundreds of thousands of them—yes, and here are some of the old ones, the parent yeasts I sowed in the bottle yesterday.” He wanted to rush out and tell some one, but he held himself—he must find out something more—he got some of the soup from the fatal bottle into a retort, to find out whether his budding beings had made alcohol. “Liebig is wrong—albumen isn't necessary—it is yeasts, the growth of yeasts that ferments sugar.” And he watched trickling tears of alcohol run down the neck of the retort. He spent the next weeks in doing the experiment over and over, to be sure that the yeasts would keep on living, to be certain that they would keep on making alcohol. He transferred them monotonously, from one bottle to another—he put them through countless flasks of this same simple soup of ammonia salt and sugar in water and always the yeasts budded lustily and filled the bottles with a foamy collar of carbonic acid gas. Always they made alcohol! This checking-up of his discoveries was dull work. There was not the excitement, the sleepless waiting for a result he hoped for passionately or feared terribly would not come.

  His new fact was old stuff by now but still he kept on, he cared for his yeasts like some tender father, he fed them and loved them and was proud of their miraculous work of turning great quantities of sugar into alcohol. He ruined his health watching them and he violated sacred customs of all good middle-class Frenchmen. He writes of how he sat down before his lens at seven in the evening—and this is the dinner hour of France!—he sat down to watch and see if he could spy on his yeasts in the act of budding. “And from that time,” he writes, “I did not take my eye from the microscope.” It was half past nine before he was satisfied that he had seen them bud. He made vast crazy tests that lasted from June until September to find out how long yeasts would keep at their work of turning sugar into alcohol, and at the end he cried: “Give your yeasts enough sugar, and they will not stop working for three months, or even more!”

  Then for a moment the searcher in him changed into a showman, an exhibitor of stupendous surprises, a missionary in the cause of microbes. The world must know and the people of the world must gasp at this astounding news that millions of gallons of wine in France and boundless oceans of beer in Germany are not made by men at all but by incessantly toiling armies of creatures ten-billion times smaller than a wee baby!

  He read papers about this and gave speeches and threw his proofs insolently at the great Liebig's head—and in a little while a storm was up in the little Republic of Science on the left bank of the Seine in Paris. His old Professors beamed pride on him and the Academy of Sciences, which had refused to elect him a member, now gave him the Prize of Physiology, and the magnificent Claude Bernard—whom Frenchmen called Physiology itself—praised him in stately sentences. The next night, Dumas, his old professor—whose brilliant lectures had made him cry when he was a green boy in Paris—threw bouquets at Pasteur in a public speech that would have made another man than Pasteur bow his head and blush and protest. Pasteur did not blush—he was perfectly sure that Dumas was right. Instead he sat down proudly and wrote to his father:

  “Mr. Dumas, after praising the so great penetration I had given proof of. . . added: 'The Academy, sir, rewarded you a few days ago for other profound researches; your audience this evening will applaud you as one of the most distinguished professors we possess.' All that I have underlined was said in these very words by Mr. Dumas, and was followed by great applause.”

  It is only natural that in the midst of this hurrahing there was some quiet hissing. Opponents began to rise on all sides. Pasteur made these enemies not entirely because his discoveries stepped on the toes of old theories and beliefs. No, his bristling curious impudent air of challenge got him enemies. He had a way of putting “am-I-not-clever-to-have-found-this-and-aren't-all-of-you-fools-not-to-believe-it-at-once” between the lines of all of his writings and speeches. He loved to fight with words, he had a cocky eagerness to get into an argument with every one about anything. He would have sputtered indignantly at an innocently intended comment on his grammar or his punctuation. Look at portraits of him taken at this time—it was 1860—read his researches, and you will find a fighting sureness of his perpetual rightness in every hair of his eyebrows and even in the technical terms and chemical formulas of his famous scientific papers.

  Many people objected to this scornful cockiness—but some good men of science had better reasons for disagreeing with him—his experiments were brilliant, they were startling, but his experiments stopped short of being completely proved. They had loopholes. Every now and then when he set out confidently with some of his gray specks of ferment to make the acid of sour milk, he would find to his disgust a nasty smell of rancid butter wafting up from his bottles. There would be no little rods in the flask—alas—and none of the sour-milk-acid that he had set out to get. These occasional failures, the absence of sure-fire in these tests gave ammunition to his enemies and brought sleepless nights to Pasteur. But not for long! It is not the least strange thing about him that it didn't seem to matter to him that he never quite solved this confusing going wrong of his fermentations; he was a cunning man—instead of butting his head against the wall of this problem, he slipped around it and turned it to his great fame and advantage.

  Why this annoying rancid butter smell—why sometimes no sour-milk-acid? One morning, in one of his bottles that had gone bad, he noticed another kind of wee beasts swimming around among a few of the discouraged dancing rods which should have been there in great swarms.

  “What are these beasts? They're much bigger than the rods—they don't merely quiver and vibrate—they actually swim around like fish; they must be little animals.”

  He watched them peevishly, he had an instinct they had no business there. There were processions of them hooked together like barges on the River Seine, strings of clumsy barges that snaked along. Then there were lonely ones tha
t would perform a stately twirl now and again; sometimes they would make a pirouette and balance—the next moment they would shiver at one end in a curious kind of shimmy. It was all very interesting, these various pretty cavortings of these new beasts. But they had no business there! He tried a hundred ways to keep them out, ways that would seem very clumsy to us now, but just as he thought he had cleaned them out of all his bottles, back they popped. Then one day it flashed over him that every time that his bottles of soup swarmed with this gently moving larger sort of animal, these same bottles of soup had the strong nasty smell of rancid butter.

  So he proved, after a fashion, that this new kind of beast was another kind of ferment, a ferment that made the rancid-butter-acid from sugar; but he didn't nail down his proof, because he couldn't be sure, absolutely, that there was one kind and only one kind of beast present in his bottles. While he was a little confused and uncertain about this, he turned his troubles once more to his advantage. He was peering, one day, at the rancid butter microbes swarming before his microscope. “There's something new here—in the middle of the drop they are lively, going every which way.” Gently, precisely, a little aimlessly, he moved the specimen so that the edge of the drop was under his lens. . . “But here at the edge they're not moving, they're lying round stiff as pokers.” It was so with every specimen he looked at. “Air kills them,” he cried, and was sure he had made a great discovery. A little while afterward he told the Academy proudly that he had not only discovered a new ferment, a wee animal, that had a curious trick of making stale-butter-acid from sugar, but besides this he had discovered that these animals could live and play and move and do their work without any air whatever. Air even killed them! “And this,” he cried, “is the first example of little animals living without air!”

  Unfortunately it was the third example. Two hundred years before old Leeuwenhoek had seen the same thing. A hundred years later Spallanzani had been amazed to find that microscopic beasts could live without breathing.

  Very probably Pasteur didn't know about these discoveries of the old trail blazers—I am sure he was not trying to steal their stuff—but as he went up in his excited climb toward glory and toward always increasing crowds of new discoveries, he regarded less and less what had been done before him and what went on around him. He re-discovered the curious fact that microbes make meat go bad. He failed to give the first discoverer, Schwann, proper credit for it!

  But this strange neglect to give credit for the good work of others must not be posted too strongly against him in the Book of St. Peter, because you can see his fine imagination, that poet's thought of his, making its first attempts at showing that microbes are the real murderers of the human race. He dreams in this paper that just as there is putrid meat, so there are putrid diseases. He tells how he suffered in this work with meat gone bad; he tells about the bad smells—and how he hated bad smells!—that filled his little laboratory during these researches: “My researches on the fermentations have led me naturally toward these studies to which I have resolved to devote myself without too much thought of their danger or of the disgust which they inspire in me,” and then he told the Academy of the hard job that awaited him; he explained to them why he must not shrink from it, by making a graceful quotation from the great Lavoisier: “Public usefulness and the interests of humanity ennoble the most disgusting work and only allow enlightened men to see the zeal which is needed to overcome obstacles.”

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  So he prepared the stage for his dangerous experiments—years before he entered on them. He prepared a public stage-setting. His proposed heroism thrilled the calm men of science that were his audience. As they returned home through the gray streets of the ancient Latin Quarter they could imagine Pasteur bidding them a farewell full of emotion, they could see him marching with set lips—wanting to hold his nose but bravely not doing it—into the midst of stinking pestilences where perilous microbes lay in wait for him. . . It is so that Pasteur proved himself much more useful than Leeuwenhoek or Spallanzani—he did excellent experiments, and then had a knack of presenting them in a way to heat up the world about them. Crave men of science grew excited. Simple people saw clear visions of the yeasts that made the wine that was their staff of life and they were troubled at nights by thoughts of hovering invisible putrid microbes in the air. . .

  He did curious tests that waited three years to be completed. He took flasks and filled them part way full with milk or urine. He doused them in boiling water and sealed their slender necks shut in a blast flame—then for years he guarded them. At last he opened them, to show that the urine and the milk were perfectly preserved, that the air above the fluid in the bottles still had almost all of its oxygen; no microbes, no destruction of the milk! He allowed germs to grow their silent swarms in other flasks of urine and milk that he had left unboiled, and when he tested these for oxygen he found that the oxygen had been completely used up—the microbes had used it to burn up, to destroy the stuff on which they fed. Then like a great bird Pasteur spread his wings of fancy and soared up to fearsome speculations—he imagined a weird world without microbes, a world whose air had plenty of oxygen, but this oxygen would be of no use, alas, to destroy dead plants and animals, because there were no microbes to do the oxidations. His hearers had nightmare glimpses of vast heaps of carcasses choking deserted lifeless streets—without microbes life would not be possible!

  Now Pasteur ran hard up against a question that was bound to pop up and look him in the face sooner or later. It was an old question. Adam had without doubt asked it of God, while he wondered where the ten thousand living beings of the garden of Eden came from. It was the question that had all thinkers by the ears for a hundred centuries, that had given Spallanzani so much exciting fun a hundred years before. It was the simple but absolutely insoluble question: Where do microbes come from?

  “How is it,” Pasteur's opponents asked him, “how is it that yeasts appear from nowhere every year of every century in every corner of the earth, to turn grape juice into wine? Where do the little animals come from, these little animals that turn milk sour in every can and butter rancid in every jar, from Greenland to Timbuctoo?”

  Like Spallanzani, Pasteur could not believe that the microbes rose from the dead stuff of the milk or butter. Surely microbes have to have parents! He was, you see, a good Catholic. It is true that he lived among the brainy skeptics on the left bank of the Seine in Paris, where God is as popular as a Soviet would be in Wall Street, but the doubts of his colleagues didn't touch Pasteur. It was beginning to be the fashion of the doubters to believe in Evolution: the majestic poem that tells of life, starting as a formless stuff stirring in a steamy ooze of a million years ago, unfolding through a stately procession of living beings until it gets to monkeys and at last—triumphantly—to men. There doesn't have to be a God to start that parade or to run it—it just happened, said the new philosophers with an air of science.

  But Pasteur answered: “My philosophy is of the heart and not of the mind, and I give myself up, for instance, to those feelings about eternity that come naturally at the bedside of a cherished child drawing its last breath. At those supreme moments there is something in the depths of our souls which tells us that the world may be more than a mere combination of events due to a machine-like equilibrium brought out of the chaos of the elements simply through the gradual action of the forces of matter.” He was always a good Catholic.

  Then Pasteur dropped philosophy and set to work. He believed that his yeasts and rods and little animals came from the air—he imagined an air full of these invisible things. Other microbe hunters had shown there were germs in the air, but Pasteur made elaborate machines to prove it all over again. He poked gun cotton into little glass tubes, put a suction pump on one end of them and stuck the other end out of the window, sucked half the air of the garden through the cotton—and then gravely tried to count the number of living beings in this cotton. He invented clumsy machines for getting these microbe-loaded b
its of cotton into yeast soup, to see whether the microbes would grow. He did the good old experiment of Spallanzani over; he got himself a round bottle and put some yeast soup in it, and sealed off the neck of the bottle in the stuttering blast lamp flame, then boiled the soup for a few minutes—and no microbes grew in this bottle.

  “But you have heated the air in your flask when you boiled the yeast soup—what yeast soup needs to generate little animals is natural air—you can't put yeast soup together with natural unheated air without its giving rise to yeasts or molds or torulas or vibrions or animalcules!” cried the believers in spontaneous generation, the evolutionists, the doubting botanists, cried all Godless men from their libraries and their armchairs. They shouted, but made no experiments.

  Pasteur, in a muddle, tried to invent ways of getting unheated air into a boiled yeast soup—and yet keep it from swarming with living sub-visible creatures. He fumbled at getting a way to do this; he muddled—keeping all the time a brave face toward the princes and professors and publicists that were now beginning to swarm to watch his miracles. The authorities had promoted him from his rat-infested attic to a little building of four or five two-by-four rooms at the gate of the Normal School. It would not be considered good enough to house the guinea-pigs of the great Institutes of to-day, but it was here that Pasteur set out on his famous adventure to prove that there was nothing to the notion that microbes could arise without parents. It was an adventure that was part good experiment, part unseemly scuffle—a scuffle that threatened at certain hilariously vulgar moments to be settled by a fist fight. He messed around, I say, and his apparatus kept getting more and more complicated, and his experiments kept getting easier to object to and less clear, he began to replace his customary easy experiments that convinced with sledge-hammer force, by long drools of words. He was stuck.