Courtesy of the Mises.org Blog, read the article named "Scott and Scurvy".
With the specific example of scurvy, it is shown how a perfectly working and proven cure can be forgotten and how a series of wrong, but plausibly seeming theories needs to be overcome before the right one is discovered. For a much more recent example, note the causes of ulcers. Or see the example on freezing water.
Not to blame the medicine (or other sciences), it can be pointed out, that less than a century ago it was full of what we can consider today quacks and charlatans, some of them great authorities and scientists. And wrong concepts can easily survive even today. Luckily, medicine has tools and methods, which it can use to improve it chances to find better answers and recognize the wrong answers - note that they are chances, no guarantees.
Medicine may not be a very exact science, with much reserved for the individual reactions and special features of different organisms, but it can conduct experiments and trials and so analyse its theories - and these experiments have some validity. But in the science of economics, there are no such experiments available. There are no laboratories, and the results of repeated 'experiments' will necessarily differ, since the starting conditions will be different and the people will behave differently. (This is not even to speak of other motivations to pursue specific theories...)
To put it short, economics can be easily full of quacks and charlatans even today.