WE ALL encounter the medical profession at certain times in our lives, whether it`s for birth, death, broken limbs, or sorting out a painful past. Canadians benefit from a system that has evolved in a unique way, as effectively presented in Canadian Health Care and the State: A Century of Evolution (McGill-Queen`s, 241 pages, $44.95 cloth), edited by C. David Naylor. The first of eight essays, "Medical Science and Social Criticism," by Colin D. Howell, sets the tone. It concerns Alexander Peter Reid, a major influence in the later part of the last century who, while expounding hygiene and progressive reform of a primitive healthcare system, also entertained quaint Victorian theories as to the causes of mental illness. Some of the essays contain stories that are hair-raising, to say the least. In "A Necessary Nuisance" Judith Young, a former head nurse at the Hospital for Sick Children in Toronto, writes that during the first half of this century at HSC the working and poor classes, considered "drunken and tainted parents," were restricted to visiting their children one hour on Sundays - a practice that lasted until the 1950s - while the more affluent had free access; and immediately after the Second World War, nurses were said to have to "kill for a diaper," and infant mortality was high on the overcrowded wards. Two of the essays, by the historians Desmond Morton and Terry Copp, focus on the two world wars of this century and the strides made in disease control in the former and psychiatry in the latter. This thought-provoking collection should be required reading for those interested not only in health care, but also in historical and sociological views of our society.