He was publicly lampooned as an imaginary "Dr Phantasus".[1] But Ehrlich's rationale was that the chemical structure called side chain forms antibodies that bind to toxins (such as pathogens and their products); similarly, chemical dyes such as arsenic compounds could also produce such side chains to kill the same microbes. This led him to propose a new concept called "side-chain theory". (Later in 1900, he revised his concept as "receptor theory".)