By MIKE MAGEE

In 1872, English mathematician and sometimes poet, Augustus de Morgan, wrote this catching rhyme: “Great fleas have little fleas upon their backs to bite ‘em, And little fleas have lesser fleas, and so ad infinitum.”

This truism about competition among species for access to nutrition and reproduction could have come in handy to Napoleon 60 years earlier when he tragically underestimated his enemies will to live. It wasn’t so much the stubborn Russians as it was microbes that were his undoing.

When he launched his invasion with a staggering force of 615,000 men, 200,000 horses, and 1,372 mobile guns, he appeared unstoppable. But on his way to Moscow, (according to Tolstoy’s account of the misadventure in “War and Peace”) he lost 130,000 men to Shigella dysentery. Confronted with harsh weather and a Russian force that refused to engage in defense of Moscow, Napoleon lost 2/3 of his remaining retreating force to Typhus, carried by Rickettsia prowazekki, housed in body lice embedded in his soldiers rancid clothing.

Under more favorable circumstances, the soldiers immune systems would have been their ally. Human bioengineering has evolved side by side with pathogenic microbes determined to chemically out smart their human hosts.

Humans rely on innate and adaptive mechanisms to detect and destroy pathogens. But to do so while sparing their own cells, they must be able to distinguish self from non-self. And they must adapt and remember, producing long-lived immune cells and protein receptors that allow them to “capture” and destroy repeat offenders.

If the system experiences a breakdown in self-tolerance, the protective processes may over-shoot and result in a chronic inflammatory response that destroys healthy tissues and marks the emergence of auto-immune diseases.

One special circumstance where immuno-tolerance is both normal and essential is maternal self-suppression during pregnancy which allows two separate immunologic organisms to survive intimate relations side-by-side.