[quote=@Dinh AaronMk] Inform the peasants they do not need the shackles of their lords and plot a peasant revolt against the feudal aristocracy. And then in doing so probably wake up the progressive peasants who'll just say, "wait for the king's son, I hear he's got some good ideas". [/quote] i bet wat tyler is just a time traveling you then. [quote=@catchamber] Sure, there are also penicillium strains native to the Americas, but can you identify and refine them without using the internet? It's one thing to say it's possible, but it's another to actually know how to do these things. As for disease: [url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1071659/]I sure hope you're immune to staphylococcus, streptococcus, syphilis, and tuberculosis[/url], especially strains from 500 to 1500 years ago. I also hope the locals are immune to all the bacteria inside of you. The pathogenic sword cuts both ways. Also, as population density increases from urbanization, you'll have to deal with those pesky plagues. Good luck bootstrapping technology while everyone is dropping like flies. [/quote] We have natural protections against staph and strep because both of those are bacteria that live in and on human beings naturally. A staph or strep infection happens when that immunity fails and the bacteria get out of control. Syphilis isn't a problem if you are going to medieval Europe, because syphilis is a new world disease. I don't know if the former two have evolved to be too different from past strains. Tuberculosis would be more of a problem though... That being said, bringing and successfully propagating ideas like sanitation and germ theory might do wonders. Modern medicine is important, but the biggest reason the west is so much more healthier now is because of how we use our basic understanding of these things.