Resource to search for free e-books

one of the lecturers tolв me about the nice portal, where you can search and download free e-books: Rapid Ok - file search engine It has a lot of free e-book downloads and yet very simple interface, so you could take a look and see what you can find concerning your subject of interest. Should you find some interesting stuff about blood system, and especially about red cells, then feel free to share with me in comments :)