In entering upon the consideration of a subject so important, one cannot but feel surprised at the very general obscurity which envelops a question upon which so large a mass of accurate detail has been collected. In looking for the cause of this unsatisfactory state of affairs, it would appear to be due to a lack of appreciation by one set of workers, of the methods pursued by another, and this in two directions. In the first place, the student of normal cell life relegates aberrant vital processes entirely to the domain of pure pathology; whilst the pathologist, relying mainly on organs as a whole for his views on function, normal and abnormal, is apt to ignore the value of the study of the cell processes as carried on under normal conditions.