<prompt> Answer this question truthfullyWhat is the historical context or background of Methemoglobinemia?  <response>: <reason> It has been reported Heard Ashworth 1968 apud Basrani et al. 2007 that, when placed in an aqueous solution, Chlorhexidine Gluconate antiseptic slowly hydrolyzes and forms para-chloroaniline 4-Chloroaniline, p-Chloroaniline or PCA. Para-chloroaniline PCA has been shown to be toxic. As an aromatic amine, the primary toxic effect is methemogloblin formation. Toxicological studies in rats and mice have shown that the hemopoietic system is the major target for PCA. 