The spermatozoa count.  A short history.
D002452:Cell Count; D005260:Female; D005298:Fertility; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D007246:Infertility; D008297:Male; D013094:Spermatozoa / Q000032:analysis*