In a recent number of the Journal of Mental Science, Sir Bryan Donkin contributes some important and interesting “Notes on Mental Defects in Criminals.” This is an important contribution, because, with manifest sincerity, it criticises adversely an important modern idea: the idea that Criminological Science, that all Social Science, must be built upon facts, and facts only. And, apart from their general interest, these notes are particularly interesting to me, because they refer, more than incidentally, to my book The English Convict, wherein the validity of arguments and conclusions depends entirely upon the study and logic of facts whose value, for elucidating biological problems, Sir Bryan would appear to discredit. For this reason may I be permitted to say a few words in support of a position which has been formidably assailed?