There are three factors of importance which have a direct bearing on the pathologic significance of any given laboratory test: (1) the accuracy of the technical procedure used in the test; (2) the establishment of normal limits within which variations may occur which have no especial significance, and (3) the interpretation of the findings obtained. In establishing the normal limits attention must be given to the obtaining of a large enough aggregate of samples from a truly representative group to warrant acceptance of the limits found as a fair representation of normal variations. To be of any real importance any interpretation of an abnormal finding must be based on a sound comprehension of the pathogenesis of the disease process under consideration.
All these factors are of real importance when use is made of the leukocyte count. In a previous article1 the fact was emphasized that a uniformity of technic