Encephalomyelitis and the clinical pathologist.

Twenty-one years ago I had the honour of addressing this Association in a short Presidential address and I then chose for my theme the opportunity which clinical pathology gave for studying the natural history of diseases. This old term "natural history" recalls Gilbert White's immortal "Natural History of Selbourne." It distinguishes study by observation of naturally occurring biological phenomena from study by planned experiments and thus well describes the special field of the clinical pathologist. Just as Gilbert White described not only the form and colour of birds but also their habits of feeding, nesting, and migration , so the clinical pathologist studies a disease as a whole, its aetiology, its clinical, biochemical and haematological manifestations, and, finally, in some cases, the changes which it produces in the organs of the body. For many of us this last study has such a special fascination that we tend, as we grow older, to devote ourselves more exclusively to it. But, if in our earlier work, we looked at diseases from the broader point of view of the clinician and clinical pathologist, we shall be less likely to lose sight of these wider aspects when we specialize. It is in this broad manner that I ask you to consider the natural history of encephalomyelitis. This group of diseases is fortunately rare in Britain. We owe this partly to our position as an island and partly to our climate, which is seldom warm enough to make our indigenous mosquitoes very active or to encourage other forms of biting insects such as wood ticks. As a result we are almost free from insect-borne forms of encepha-litis. The only exception is the occasional human case of louping-ill. The only virus disease of the nervous system which has caused much trouble is poliomyelitis and even this disease seems to be discouraged by our climate and only in rare summers approaches anything like epidemic proportions. When therefore the occasional case of encephalomyelitis turns up it arouses little interest and we may be satisfied with this general diagnosis and make no attempt to trace the type of disease. B In looking at the natural history of any disease we must learn from the past. I should like therefore to say something of my own experience with this group of diseases. This goes back to 1917 when I saw my first two cases of encephalitis lethargica, in a convalescent …