THE Registrar-General has recently issued the second of the monographs dealing with medical and population subj acts (Sickness in the Population of England and Wales in 1944– 47 ; H.M. Stationery Office. 1s. For more than a century the statistics of the General Register Office have provided a basis for attacks by medical science on the killing diseases ; but it is only in recent years that an attempt has been made on a national scale to measure ill-health which does not necessarily cause death, but which leads to great economic loss as well as individual and social disturbance. Before ill-health can be measured it must be defined, and for any published morbidity statistics to have real meaning the terms used should command general acceptance. In the present stage of development of this subject terminology is neither precise nor uniform, and here the author of the monograph, Dr. Percy Stocks, chief medical statistician to the General Register Office, makes an attempt to standardize terminology by describing in detail the terms he uses in the interpretation of his material. He then examines the value and limitations, as indices of morbidity, of information derived from notifications of infectious diseases, from the Survey of Sickness, carried out monthly since 1943, and from statistics of special food allowances given for certain diseases.