ON JANUARY 20, 1942, Nazi leaders gathered at a lakeside villa in Berlin to plan the “Final Solution of the Jewish question.” Half-Jews, or first-degree Mischlinge, they concluded, were to be treated as full Jews, while quarter-Jews would be assimilated into Aryan society. Although Warburg had managed to keep his position at his institute, he remained a first-degree Mischling and so was on the wrong side of the new divide.
The decisions made that January afternoon might have meant the end for Warburg, but some officials continued to push for sterilizing rather than deporting half-Jews. On March 6, senior Nazi officials gathered again, this time for a conference dedicated to the “Final Solution” of the Mischling question. At this second conference, overseen by Adolf Eichmann, attendees debated the finer points of mass sterilization. Would it be realistic, the pragmatists wondered, to sterilize tens of thousands of first-degree Mischlinge? How would they find enough hospital space? Another conference attendee noted that sterilization would not make the Mischlinge headache go away, at least not until all of the sterilized Mischlinge had died out. One Nazi in attendance later referred to the plan of waiting for first-degree Mischlinge to die as a “setback” he was prepared to endure.1
By the end of this second “Final Solution” conference, the Mischling question still had no answer, but Warburg’s situation had nevertheless changed dramatically. On the same day that the conference convened, Germany’s High Command of the Armed Forces designated Warburg’s institute “of military importance.” Whether the timing of the order was more than a coincidence is unknown.2
The order made Warburg’s life at least somewhat more secure, but he was far from safe. He remained a first-degree Mischling, and his tormentors were not yet done with him. In the fall of 1942, Rudolf Mentzel, the Nazi science official who had tried and failed to oust Warburg from his institute the year before, began sending out queries to various German scientists about Warburg’s still outstanding application for a German Blood Certificate.
Mentzel was almost certainly hoping to find information he could use against Warburg, but if the responses to Mentzel that have survived are any indication, the Nazi bureaucrat ended up profoundly disappointed. No respectable researcher could deny the importance of Warburg’s contributions to science. One response, from the Nobel Prize–winning German chemist Adolf Windaus (who did not know Warburg personally), noted that Warburg was considered “the most important physiological chemist alive.” The letter, sent in October 1942, might have forced Mentzel to give up his campaign against Warburg’s Aryanization. That same month, Warburg was made a member of the Reich Committee for the Fight against Cancer, further solidifying his standing in Nazi Germany.3
That Warburg’s application for equal status with someone of German blood was even being considered in the fall of 1942 is “amazing,” according to Beate Meyer, of the Institute for the History of German Jews. In the summer of 1942, a new order had put an immediate end to such applications, and very few exceptions were made.4
Whether Warburg’s application was ever accepted is unclear. Hans Krebs wrote that Warburg was formally reclassified as a second-degree Mischling (someone who had only one Jewish grandparent), but there are no known documents that confirm this. It is possible that Warburg achieved something even more unlikely than Aryanization: equal status with the upper crust of Nazi Germany not as a suddenly transformed Aryan but as a despised Jewish “mongrel.”
BY THE SUMMER OF 1943, Warburg and Heiss would have grown accustomed to the piercing air-raid sirens and rumbling engines of Allied bombers overhead. They may have gone into the cellar of their home or to public air-raid shelters. If they ever dared to look into the night sky, they would have seen the blinding flashes of light followed by streaks of tracer fire from German antiaircraft guns.
Warburg, still searching for a cancer cure, made another important discovery during this period: some of the enzymes required for fermenting glucose could also be detected in the blood of rats. These enzymes had no function in the blood, so Warburg concluded that they must have leaked out of other tissues. Warburg was particularly interested in one enzyme, zymohexase (now known as aldolase). He found that he could detect it at much higher levels in the blood of a rat with cancer than in the blood of a healthy rat.5
Warburg’s discovery would give rise to important diagnostic tests after the war. A 1963 textbook credited Warburg and his employee, Walter Christian, with opening up an entire field with the finding. But Warburg wasn’t interested in new lab tests. He wanted to defeat cancer, and he suspected that the zymohexase in the blood of rats with cancer wasn’t leaking from the tumor itself but from muscle tissue. The cancer, he reasoned, was somehow recruiting enzymes out of healthy muscle tissue to participate in its campaign of destruction.
Following a model of drug development pioneered by Paul Ehrlich, Warburg set a new plan of attack: He would take zymohexase from humans and inject it into healthy rabbits. The rabbits would then produce an anti-zymohexase serum that would block the enzymes and “check the cancer in its fermentation processes.”6
It was an outlandish idea, and Warburg had little time to pursue it. One morning in the summer of 1943, he arrived at his institute to find that it no longer had windows. The staff spent weeks picking up shards of glass and scattered bits of cement. When another bomb fell and did still more damage to the building, Warburg chose to leave Berlin. That, at least, was the explanation he provided for his move. It’s also possible that Warburg, even after outmaneuvering his most dedicated Nazi foes, could no longer withstand the poisonous atmosphere in Dahlem. After the war, when a Russian scientist arrived at his institute to pillage the remaining chemicals, the door was answered by an unidentified man. Warburg had fled Dahlem, the man told the Russians, because he was a Jew.7
Whatever his reasoning, Warburg was in need of a new location for his institute, and thanks once again to his influential connections, he found one in a scenic region of lakes and woods some 30 miles north of Berlin. As Jews across Europe were being packed onto trains and transported to death camps, Warburg, a homosexual with two Jewish grandparents, relocated to an elegant mansion on the grounds of a sprawling country estate.
Known simply as Liebenberg, the estate had once been owned by the closest friend of Kaiser Wilhelm, and the kaiser himself had spent many of his happiest days there. (In 1898, Theodor Herzl, the founder of modern Zionism, traveled to Liebenberg in an effort to persuade the kaiser to support a Jewish homeland in Palestine.) Hermann Göring regularly visited Liebenberg to shoot deer and wild boar. The primary residence, an enormous castle, was occupied. Warburg’s institute was set up in the estate’s lake house mansion.
Though nearly all German resources were reserved for the war effort, the Nazis nevertheless had the mansion renovated for Warburg, complete with a new roof and a transformer station. In addition to his scientific equipment and lab animals, Warburg brought along his books and antique furniture. (When additional trucks were needed, Warburg instructed one of his employees to bribe the rationing office with a bottle of distilled alcohol.)8
Liebenberg was an absurdly fortunate landing spot for Warburg under the circumstances. Though it’s unlikely that Warburg was aware of it, a cousin, Dr. Betty Warburg, had already been murdered at the Sobibor extermination camp along with her mother, Gerta. But the Emperor of Dahlem, now in exile, did not feel lucky. Warburg, anticipating Germany’s imminent collapse and surrender, retreated to his vacation home on the island of Rügen with Heiss until work at the lake house was completed. With Warburg away, his technicians were left to carry out their experiments with little guidance. Warburg planned to oversee the work via daily telephone calls, but by the last years of the war, it was difficult to secure an open line. The problem was resolved only after Heiss delivered chocolates to a local telephone operator.9
Warburg was accustomed to summer breaks at Rügen, but with the exception of the First World War, he had never been away from a laboratory bench for so long as an adult. He used the time to work on a book on heavy metals and respiration. When Hans Krebs later read the first draft, he was horrified. Warburg had filled a book ostensibly about the role of iron and other metals in cellular function with nasty asides about celebrated scientists.
Warburg hardly needed a reason for petty attacks, but his situation surely embittered him even more. In December 1943, he was denounced in an anonymous letter to the Gestapo for sabotaging the war effort—a crime punishable by death. Among other offenses, the letter accused Warburg of being anti-Germany and pro-England, of refusing to work, and of using the institute’s gasoline—a scarce resource then restricted for war-related efforts—for trips to his vacation home with Heiss. Warburg’s behavior, the letter said, was not merely detestable but “asocial”—a loosely-defined charge the Nazis used to persecute anyone who didn’t conform to public norms.
The accusation of “asocial” conduct put Warburg’s life in grave danger yet again. By 1944, some half-Jews were being assigned to labor camps. Others, accused of behaving like full Jews, had been condemned to death for the crime of “undermining the war effort.” Warburg’s enemies at the Education Ministry were still in power, and by this point in the war, the Nazis needed little excuse to murder anyone, let alone a first-degree Mischling. Upon learning that he had been denounced and was under investigation, Warburg’s dark mood turned darker still. Already predisposed to great paranoia, Warburg now had entirely legitimate grounds for suspecting everyone around him of being his enemy. Though every member of Warburg’s staff likely had more than enough evidence to have Warburg arrested, Warburg was convinced that Fritz Kubowitz, the man who had worked with him on many of his most important experiments, including some that led to his Nobel Prize, had written the letter.10
Warburg was almost certainly correct in assuming the denunciation came from one of his employees. The postmark reveals that it had been mailed near Liebenberg, and the specific examples of his crimes, such as using gasoline, would only have been known to close associates.
The letter denouncing Warburg was soon followed by a second letter, sent to the Kaiser Wilhelm Society, that included the allegation that Warburg was a homosexual. Warburg, isolated in his palace in the woods, was now overcome with Lear-like rage and indignation. Most of his employees had been with him since the start of his career. He had taught them chemistry. Their names appeared side by side with his own on his scientific papers. When Warburg said he couldn’t leave Germany in the 1930s, he had cited not his magnificent building but the impossibility of replacing these men.
Theodor Bücher, a 30-year-old German researcher training in biochemistry at Warburg’s institute, was on good terms with Warburg and attempted, with little success, to calm him down. He “felt himself persecuted,” Bücher wrote, “even persecuted to death.” In Bücher’s assessment, Warburg had become a deeply unhappy man, torn apart by the clash between “feelings of inferiority” and a “raw egocentrism.” Bücher saw Warburg try to fight back against his demons and admired the effort it took. But by 1944, the demons could not always be tamed.11
The investigation that followed Warburg’s denunciation was not the only open investigation of Warburg at the time. Seven hundred miles away in Sweden, Warburg was being considered for another Nobel Prize, for his work on coenzymes. But in 1944, international fame and prestige was of no use to the Nazis, and in any case, Hitler had forbidden Germans from accepting the award.
With his life again in jeopardy, Warburg again reached out to Walter Schoeller, his colleague who was married to Philipp Bouhler’s sister-in-law. By then, the limits of what Schoeller could do for a persecuted Jewish scientist were all too clear. In September 1942, the Nazis had arrested Wilhelm Traube, one of Germany’s most distinguished organic chemists, and planned to deport him. Schoeller was among the scientists who made pleas on Traube’s behalf, but he was too late. The Gestapo officers who arrested the 76-year-old Traube had beaten him so badly that he died in prison.
Warburg, as usual, would have far more luck than most. Philipp Bouhler, the man at the helm of the Chancellery of the Führer, visited Liebenberg himself to confirm that Warburg was working on his cure for cancer. According to one account, Warburg managed to fool Bouhler by having new experiments hastily set up.
Though the details of the Liebenberg inspection remain murky, Bücher wrote a detailed account of the aftermath. As soon as Bouhler left the building, a still-rattled Warburg invited Bücher for a walk. They strolled across the estate’s endless lawns in silence for several minutes, and then the 60-year-old Warburg turned to the young man by his side and asked him a question he was not prepared for: “Do you consider me to be asocial?”
Bücher would have understood “asocial” in the Nazi context. Warburg was asking Bücher if he thought of him as a misfit. A startled Bücher could only muster that Warburg might show more in the way of noblesse oblige. With that, Warburg’s momentary show of vulnerability was over, and he changed the subject.12
WHATEVER EXPERIMENTS he might have staged during the inspection of the institute in Liebenberg, Warburg appears to have gone back to working in earnest afterward. According to Bücher, every member of the lab, including Warburg, continued to carry out experiments in search of cancer therapies even as the Allied bombing squadrons roared overhead. For stretches of 1944, Warburg not only worked but maintained a semblance of ordinary life at Liebenberg, sometimes visiting the palatial primary residence, where the regularly scheduled “music evenings” continued even as Germany crumbled.
Once a week, Warburg reportedly had a roast goose prepared for a group of Dutch prisoners of war who had been stationed at Liebenberg. (Heiss likely did the roasting.) Toward his own staff, by contrast, Warburg felt only animosity. He was no longer speaking to Kubowitz at all. The tension, Bücher wrote, would soon arrive at “a horrifying end.”
By late 1944, millions of Soviet soldiers had gathered on the banks of Poland’s Vistula River. Hitler, meanwhile, had organized a national suicide program in the form of the Volkssturm, a poorly equipped people’s army comprised mostly of teenage boys and old men who were expected to stand as a last defense against Germany’s enemies. All German men ages 16 to 60 who weren’t currently in the military were called upon to enlist.
Because Warburg’s lab had been designated a war institute, he had the power to save his employees by informing authorities that their work was necessary for his research. And Warburg did manage to protect Bücher and Heiss. But other members of the lab were less fortunate. Their fate was in the hands of their boss, a man who had solid evidence that they had betrayed him.
Fritz Kubowitz, the employee Warburg believed had denounced him, ended up in the Volkssturm I, an assignment that was, for many, a death sentence. After being sent to the front, Kubowitz reached out to Warburg, then at his vacation home on Rügen, for help. Warburg appears to have been genuinely distraught. He began to scribble short diary entries in the back of one of his laboratory notebooks, a highly uncharacteristic act. In an entry dated February 24, 1945, Warburg justified his harsh decision on Kubowitz to himself: “You cannot denounce your superior today and ask him to save your life tomorrow.”
Erwin Negelein, the man listed as a coauthor on Warburg’s groundbreaking cancer papers in the 1920s, also ended up in Volkssturm I. On March 17, 1945, his emaciated wife arrived at Liebenberg and pleaded with Warburg to send a replacement for her husband at the front. Warburg, convinced that Negelein had played a role in denouncing him, turned her away. “I refused to intervene,” Warburg wrote. “Why should I try and send somebody else instead, in order to protect her husband?”13
Three days later, Warburg received a government order to relocate his equipment and sensitive documents before the enemy arrived. With air-raid sirens blazing at all hours and the Red Army only about 100 miles away, he retreated with Heiss to Rügen.
On April 16, 1945, the Russians crossed the Oder River and pushed west to Berlin. Within two weeks, the Red Army controlled Liebenberg and had emptied the lake house of Warburg’s equipment and treasured antique furniture. When Stalin’s soldiers made it to Rügen, they found Warburg at home. According to a secondhand report, Warburg spoke first, announcing himself as the “famous Nobel Prize winner, Professor Otto Warburg from Berlin.” The soldiers put down their guns.
In 1933, when the Nazis came to power, there were more than 100 scientists at the prestigious Kaiser Wilhelm institutes who qualified as Jewish, according to Nazi definitions at that time. Otto Warburg was the only one to maintain his position until the very end.14
WHILE SOME NAZI initiatives against cancer, such as mass screenings for cervical and uterine cancers, had to be abandoned in the last years of the war, others, including experiments involving food dyes, hormones, tobacco, and asbestos, continued without interruption.
In a memo to senior Nazi medical officials sent early in March 1945—when the Allies had Berlin surrounded and were preparing to end the Nazi regime—Himmler proposed a new cancer project: he wanted them to look into the mystery of why concentration camps had “no people with cancer.” Himmler even asked the medical officials to calculate how many cancer cases could have been expected among the 700,000 prisoners, given the rates in the general population. Within three months of sending off this memo, Himmler had been captured. He poisoned himself and died while being examined by a British doctor.15
Cancer would remain on Hitler’s mind to the end as well. On November 5, 1941, with the prospect of an easy victory against the Red Army looking increasingly unlikely, Hitler sat down for lunch at his headquarters in eastern Prussia with several guests, including his dentist, Hugo Blaschke, a man who disliked Hitler not because he was a mass murderer but because his teeth were so awful.
Any sane military commander would have been focused exclusively on the war at that moment. Hitler had something else to discuss. Over the course of the meal, Hitler declared that Caesar’s soldiers had followed vegetarian diets and that the Vikings would never have managed their legendary expeditions if they had been able to preserve meat and thus eat it on their journeys. He also claimed that humans had likely lived longer in the past, perhaps from 140 to 180 years of age, and that the decline began when sterilized food “replaced the raw elements in [their] diet.”
Blaschke was a vegetarian himself and believed that the shape of human teeth revealed that our ancestors were herbivores. But even he was left “speechless.” And Hitler was only warming up. People live longer in countries like Bulgaria, where polenta and yogurt are popular dishes, Hitler told his perplexed guests. (Yogurt, according to a popular theory, could cleanse the colon of cancer-causing bacteria.)16
Hitler then launched into a diatribe in which he managed to mangle Erwin Liek’s thinking on diet and cancer with his own unique mélange of nonsense and fantasy:
The fact that man subjects his foodstuffs to a physicochemical process explains the so-called “maladies of civilization.” If the average term of life is at present increasing, that’s because people are again finding room for a naturistic diet. It’s a revolution. . . . It’s not impossible that one of the causes of cancer lies in the harmfulness of cooked foods. We give our body a form of nourishment that in one way or another is debased. At present the origin of cancer is unknown, but it’s possible that the causes that provoke it find a terrain that suits them in incorrectly nourished organisms. . . . Nature, in creating a being, gives it all it needs to live. If it cannot live, that’s either because it’s attacked from without or because its inner resistance has weakened. In the case of man, it’s usually the second eventuality that has made him vulnerable. A toad is a degenerate frog. Who knows what he feeds on? Certainly on things that don’t agree with him.17
At the time, Hitler was following the raw-foods diet developed by the Swiss physician Max Bircher-Benner, the muesli inventor who believed that raw foods offered more direct access to the sun’s energy. (Himmler was also an admirer of Bircher-Benner.) Hitler didn’t force his guests to follow his diet of muesli, gruel, and linseed mush. But even as the Nazis were torturing and gassing their victims by the hundreds of thousands in concentration camps, he would sometimes lecture the meat eaters he dined with about the horrors of animal slaughterhouses.18
The muesli didn’t make Hitler any healthier. In addition to his usual stomach problems and terrible headaches, his vision was failing. He feared he was going blind. Despite Blaschke’s best efforts, more and more teeth were falling from the führer’s rotting gums, forcing him to eat only soft foods. Electrocardiograms indicated progressive heart disease.
At the end of 1944, doctors found another growth in Hitler’s throat and removed it. There was no evidence of cancer. It would have mattered little if there had been. With no hope left for victory, Hitler retreated to his two-story concrete bunker beneath the Reich Chancellery. Several years earlier, he had repeated his claim to Robert Koch’s mantle:
The discovery of the Jewish virus is one of the greatest revolutions that have taken place in the world. The battle in which we are engaged today is of the same sort as the battle waged, during the last century, by Pasteur and Koch. How many diseases have their origin in the Jewish virus!19
Now, trapped in his bunker, Hitler sometimes dug at imagined bacteria on his flesh with a pair of golden tweezers.
Hitler had become a horrible specter, lurking in his German underworld. His ghastly appearance—he was severely hunched with pale yellowish gray skin and lifeless eyes—startled visitors. His left hand trembled so badly he had to restrain it with his right. “Often he would just sit there with painfully distorted features,” Hitler’s valet Heinz Linge remembered.20
Christa Schroeder, one of Hitler’s secretaries, remained with him in the bunker until almost the end. Schroeder had enjoyed Hitler’s diatribes during better times. She recalled how he would fall “into poetic rapture” when talking about how his food had grown: the farmer’s arm sweeping through the air as he drops the seeds, the seeds sprouting “into a green sea of waving stems.” That image alone, Hitler once told Schroeder, “should tempt man back to nature and her produce.”
Hitler was now often too feeble to engage in his infamous histrionics and declamations. “The things he talked about became gradually more flat and uninteresting,” Schroeder remembered. He had stopped ranting to his secretary about “racial problems” or even “political questions.” In the last months of his life, Hitler had the strength left for only three topics: dog training, the stupidity of the world, and diet.21
On April 29, 1945, with the Red Army down the street from his bunker, Hitler married his longtime girlfriend, Eva Braun. The following day, he ate a vegetarian lunch of spaghetti with a raisin-cabbage salad and then retreated to his study with his new bride. At 3:30 p.m., a loud bang echoed through the underground structure. One of Goebbels’s children was playing nearby. When he heard the gunshot, he let out a shout: “That was a bullseye!”22
Hitler had left behind an ocean of blood, but inside his death chambers, the corpses left few stains. Zyklon B, the poisonous gas initially developed as an insecticide, kills by suffocation. As the molecules attach to the iron of Warburg’s respiratory ferment in place of oxygen, the fire of life flickers and goes out.