The following observations are the result of three years' work in examining the leucocytes in the various patients admitted to the Perth District Asylum. During this period the blood of 150 patients has been systematically examined, not on one or two occasions only, but often for weeks and months at a time. We have observed in medical literature observations recorded on the leucocytosis occurring in various forms of insanity in which the observer had made many observations on different patients, but as a rule limited the observations made on each individual patient to one, two, or at most three occasions. Such records are of little or no value, and would be on a par with the observations of, let us say, an astronomer who, having examined the heavens on two nights out of the 365, and having found both nights cloudy, reported that no such things as stars existed. With regard to the technique employed for the estimation of the number of leucocytes per c.mm. of blood, we have throughout employed Coles' system of counting “fields” with the counting slide of a Thoma Zeiss' hæmocytometer. Never less than thirty fields were counted for each enumeration, and frequently sixty and eighty fields were counted when extra accuracy was deemed necessary.