PREFACE
Mr Fothergill has asked me to write a short preface for his useful little work. Every year the importance of blood examination in connection with disease is increasing; and this is especially the case with Tropical Diseases. In malaria, filariasis, kala-azar, sleeping sickness, relapsing fever, and tick fever, the detection of parasites gives at once a definite diagnosis and a sure guide to treatment. Various serum-reactions are not less valuable; and blood counts are frequently of great assistance.
With regard to the last named, caution must always be urged as regards the "error of random sampling"—the number of corpuscles examined must be sufficiently large. It is to be hoped that the mathematicians will shortly tell us how many leucocytes, for instance, must be studied in making a differential leucocyte count, in order that the error shall be below any given percentage; but at present this point is not sufficiently considered; and we actually hear of differential counts being
