Petit canard, grand canard

The flu pandemic of 1918 was horrific. Millions of people died (by some estimates 4% of the world population), and the medical establishment worked feverishly to find a cause and a treatment. There were many dead-ends in the search for the cause of the flu. One of the most enduring errors was the attribution of the pandemic to a bacterium called Haemophilus influenzae. It turned out that the flu was actually caused by a virus rather than a bacterium, but H. flu is still an important discovery. The fight against influenza was in many ways successful (although too late for the 1918 pandemic)---it led to the discovery of influenza and many other viruses, and the development of effective influenza vaccines. It is analogous to the discovery of HIV and the advances in science and medicine pioneered by HIV researchers. Influenza birthed the field of virology.

But what if we had stopped at one of our dead ends? What if we had held to the belief that H flu caused influenza, or that HTLV-1 caused AIDS? In science, dead-ends usually reveal themselves---eventually. As new discoveries fail to appear, scientists re-examine their underlying assumptions. H flu was found in many flu victims, but not all. Other researcher found that fluids that were run through filters that stopped bacteria were still infectious (in human volunteers!), leading them to conclude that there must be an infectious particle smaller than a bacterium. A quarter of a century after the Great Influenza pandemic, effective vaccines against influenza were in production. 

While the world was torn by the first "modern" war, and influenza destroyed military and civilian populations, doctors were trying everything that might help.  In the U.S., sera and vaccines against various agents such as pneumococcus were produced and used with some efficacy, but many other immunologic treatments were dead-ends.  One of these dead-ends was named Oscillococcinum.

A French doctor, Joseph Roy, was one of the witnesses to the 1918
pandemic who worked to find a cause.  Unfortunately, his thinking was
rooted in a mix of modern ideas and ancient---the knowledge that there
were bacteria that caused disease, and the ancient vitalist
ideas of the previous centuries.  He believed that he observed in flu
victims, and the victims of many other diseases, an unusual bacterium
which was round ("coccus") and appeared to vibrate ("oscillate"). 
Anyone who has spent significant time on a light microscope knows that
there's plenty of oscillation---it's called "Brownian motion" and is
not a characteristic of any particular object under the lens but of the
medium itself.  Roy, using the modern terms and equipment but not
modern knowledge, felt that this "new bacterium", which he observed in
microscopic samples from nearly every infectious and non-infectious
disease, was the cause of everything.  While modern scientists were
searching for the agent of influenza and other diseases, and trying to
fulfill Koch's postulates (not a requirement, but handy) Roy was
bringing to life one of the most enduring errors in modern medicine.
Unlike the discovery of H. flu, the "discovery" of Oscillococcinum (which I'm hesitant to dignify with italics) led
not to the control of important diseases but to the world's most
popular quack remedy for influenza.

Roy and others ran with
this "discovery".  It's not clear exactly who decided to use
Oscillococcinum to fabricate a homeopathic potion, but according to at
least one source, Roy approached the French Homeopathic Laboratories in
1925 with a plan to produce his panacea from duck livers (and, of
course, lots of water).

Three quarters of a century later,
Oscillococcinum is still one of the world's most popular flu
remedies.   This, despite the fact that it is based on an erroneous
discovery of a non-existent bacterium which is "derived" from duck
livers and diluted down infinitesimally.  This is the ne plus ultra of quackery.

References

Jeffery K Taubenberger, Johan V Hultin, and David M Morenshttp.
Discovery and characterization of the 1918 pandemic influenza virus in
historical context. Antivir Ther. 2007; 12(4 Pt B): 581-591. PMCID: PMC2391305.

Nienhuys, Jan Willem,The True Story of Oscillococcinum. Homeowatch.org

Rouzé, Michel, Oscillococcinum : Le petit canard a grandi. Science, et pseudo-science, n° 221, mai-juin 1996.

Rouzé, Michel, OSCILLOCOCCINUM - Le joli grand canard, SPS n° 202, mars-avril 1993.

Jean-Marie Abgrall (2000). Algora Publishing. ed. Healing Or Stealing?: Medical Charlatans in the New Age. . ISBN 1892941511.

Barry, John M. The Great Influenza: The Epic Story of the Deadliest Plague In History, Viking Adult, 2004.