But it is not only with the physical state of prisoners and the sanitation of prisons that the medical staff is concerned. The prison Medical Officer has justly acquired a reputation as an expert in mental disease. Although a practical acquaintance with lunacy is expected of a candidate for the Medical Service, it is owing to the exceptional opportunities afforded for diagnosis of the varying and often peculiar mental states of prisoners that he is expected, and is able, to give an expert opinion, not only in the grave cases where sanity is in question, but also in those difficult and doubtful cases of mental defectiveness which are continually occurring in every mode and degree. Especially is great importance attached to the opinion of the Medical Officer of prisons as that of an unbiassed expert witness on the mental condition of cases charged with a capital offence. The growing practice of the Courts to remand for medical observation in prisons when any doubt exists as to the state of mind, has the desired result of preventing the commitment to prison of persons who would be certified to be insane almost as soon as received. Thus, twenty years ago the number certified insane after reception into prison was a little over one per cent. of the total receptions. To-day it is about half that number. It is, however, with regard to a class of prisoner, who, for want of a more precise and descriptive term, is designated "mental defective", that the Medical Officer is called upon to exercise all his vigilance and powers of diagnosis. There are persons who cannot be deemed sufficiently irresponsible as to warrant certification, but who, from obvious mental deficiency, cannot be considered fit subjects for penal discipline. In 1901, a special treatment was established for this class in local and in convict prisons. The effect of the new regulations was largely to increase the rôle and responsibility of Medical Officers in controlling the daily routine in respect of food, labour, and punishment. It was about this time that the question of the best method of dealing with mentally defective persons, other than those certified under the Lunacy and Idiots Acts, came prominently before the public, and a Royal Commission was appointed to inquire into the matter. At the same time, an attempt was made to ascertain the number of persons in prison who, on account of mental defect, were deemed unfit for ordinary penal discipline. Medical Officers were requested to note down for six months the number of persons received into their respective prisons who, in their opinion, were of such a low order of intelligence as would be likely, by want of normal self-control, to get into mischief, or commit crime. The result was that 3 per cent. of both sexes of the total number of prisoners received were shown to fall within this category. Writing on this subject in 1912, Sir Herbert Smalley, until lately the Head of the Prison Medical Service, states:--