This is the 50th anniversary year of the announcement of Jonas Salk's polio vaccine, as you've probably been noticing. There a new book out on the discovery, and plenty of newspaper and magazine articles.

I'll save comment on the vaccine (and Salk himself) for another time. What got me thinking was an incident during the late phases of of the research (which was recounted in a recent article in Smithsonian magazine, taken from the book mentioned above.)

Salk and his team were injecting patients who had already had polio with their vaccine candidates, hoping to show a fresh antibody response. Blood samples were taken after a few days, and the corresponding blood serum was added to a cell culture along with fresh virus and a dye, Phenol Red. If the cells lived - that is, if there were enough antibodies in the serum to inactivate the virus - they would clear the dye color to yellow as the medium became more acidic. If they died, the red color would remain. (This was an assay developed by Julius Youngner. You can see the two colors of Phenol Red here.)

On the morning that the test results were ready for their most promising vaccine candidate, the rack of cell culture tubes showed up completely yellow. There was much celebrating, but Salk finally turned to everyone and said "OK, now let's make sure that we can do it again."

Good for him, I thought when I read that. My fellow researchers will recognize Salk's comment as that of someone who knew his way around a lab. Some of the best scientific advice that you can get is don't trust anything until you've done it at least twice. All kinds of ridiculous stuff happens sporadically, and you'll go crazy if you react to all of it. I've been kicked around like a soccer ball by "N of one" data too many times myself. Nope, don't break out the party hats until the second experiment works, and don't despair until the second one fails.