The Supreme Leader of Iran—not that nutcase I’m-a-dinner-jacket, but the more sober Ayatollah Ali Khamenei—told a crowd on Wednesday that Israel is a cancerous tumor.

He compared Obama to Bush and the U.S. to Satan, warning the new administration that, "Change means giving up your satanic, coercive and aggressive ways and instead adopting more human morals.” Israel and the U.S. are both “Satans” of different sizes, but the “cancerous tumor” metaphor is reserved for the Jewish state.

It extends a long history of disease-related attributions applied to the Jewish people. In the 19th century it was widely agreed that Jews carried certain medical conditions so much more than others did that you could call them Jewish diseases. This began before Hitler was born, but it was in the air while he was growing up.

Syphilis and tuberculosis and were two of the “Jewish diseases,” and obviously could be given to others, making the Jews even more dangerous than they would be just on the grounds of wanting to rule the world. Syphilis of course had moral implications, and suggested depraved Jewish men not only defiling but crippling pure Aryan women. But TB too had a moral dimension, since it was associated with weakness, and Jews were considered weak in more ways than one.

They supposedly had neurasthenia, which today we might call an extreme form of neurosis or a mixture of anxiety and depression, but in those days it had connotations of moral laxity and laziness. We don’t think of it as communicable, but before the germ theory of disease was understood, many believed that neurasthenia could be conveyed by Jews to others, at least by psychologically weighing down and leading astray right-thinking, hard-working, healthy Christians.

Obesity, diabetes, flat feet—important since the claim kept Jews from serving in Europe’s armies—and even foetor Judaica, a distinctively Jewish bad smell, were accepted as conditions that Jews had much more of than anyone else. Amazingly, both Jewish and non-Jewish physicians endorsed this picture as medical reality. Even the Jewish nose was considered a biological defect, and after the 1890s could be surgically fixed to make a Jew look “normal,” with untold psychiatric and social benefits.

But the great step was to see the Jews themselves as the disease, bringing all their physical, mental, and moral weakness to the nations of Europe by racial mixing.

This idea culminated at the end of the century in Houston Stewart Chamberlain’s book, Foundations of the Nineteenth Century, published in 1899. (Though English by birth, he first published the book in German.) He later wrote Race and Nation, making clear the racial “history” of two millennia and trying to prove that the fall of nations could be explained by the importing of Jews, while nations rose again by getting rid of them.

These works greatly influenced the Nazis (Chamberlain himself joined the Nazi party), and Heinrich Himmler, head of the SS, wrote in his diary after reading Chamberlain, “It is true and one has the impression that it is objective, not just hate-filled anti-Semitism. Because of this it has more effect. These terrible Jews…”

By the 1930s these theories were not just history but “science,” complete with anthropological institutes and training programs throughout Germany. Children were taught how to identify Jews, using the most up-to-date methods of racial classification. Countless publications from articles in scientific journals to anti-Semitic tracts and even cartoons spread throughout Germany and then throughout German-occupied Europe the idea of Jews as a disease contaminating civilization.

A cartoon in the Nazi publication Der Stürmer was typical but especially revealing. It showed a large microscope with a field blown up to illustrate what was glimpsed under the instrument: tiny hammer-and-sickle symbols, triangles representing homosexuals, and most of all, Stars of David. The picture is titled, “Infectious Germs.” And below it is a poem:

With his poison, the Jew drags

Weaker peoples’ burdened blood,

So a disease-picture appears

That speeds them downward.

But our report resounds:

The blood is clean. We’re healthy!

When Joseph Mengele, M.D., Ph.D., made selections for the gas chambers, he signed an order to ensure that the murders were medically justified—essentially prescriptions for preserving the health of the Aryan peoples by eliminating the Jewish “germs.”

So when Ayatollah Khamenei calls Israel a cancerous tumor, he follows a time-honored tradition of associating Jews with deadly disease. And the consequences are the same. Iran’s president, Ahmadinejad, has repeatedly called for wiping Israel off the map. Obviously, if you have a cancerous tumor, you want to cut it out.

Also this week, the head of Iran’s military said in a speech that his country has missiles that can reach any nuclear facility in Israel, and that no amount of international pressure will prevent Iran from completing its nuclear program.

Once again, a medical metaphor is brought to bear on the minds of millions to convince them that the Jews don’t merely have a disease, they are a disease, and one that can only be cured by extermination.