~Myelogenic leukæmia~ presents a picture that is different in every particular. In former years the distinction between myelogenic leukæmia and simple leucocytosis offered great difficulties. These conditions were regarded as different stages of one and the same pathological process, and when the proportion of white to red corpuscles exceeded a certain limit (1:50) it was said that leucocytosis ceased, and leukæmia began. By the aid of the analytic colour methods the fundamental difference between the two conditions was first disclosed. Leucocytosis is now recognised to be chiefly an increase of the normal polynuclear neutrophil leucocytes; whereas myelogenic leukæmia brings elements into the blood that are abnormal. The cells here introduced are so characteristic as to render the diagnosis of leukæmia possible, even in the very rare cases where the total number of the white blood corpuscles is not to any extent increased. The best example of which we are aware is a case observed by v. Noorden, in which the proportion of white to red was only 1:200.
Although the blood picture of myelogenic leukæmia has been so clearly drawn by Ehrlich, misconceptions and obscurities still occur in the literature. And they are due to great errors in observation. It has for instance happened that unskilled observers have regarded and worked up cases of lymphatic leukæmia as myelogenic. The apparent deviations discovered in this manner are copied, as specially remarkable, from one book to another. Through insufficient mastery of the staining method, the characteristic and diagnostically decisive elements (neutrophil myelocytes for example) are frequently mistaken. A further source productive of misconceptions lies in the circumstance that the typical leukæmic condition of the blood may essentially change under the influences of intercurrent diseases. Thus the intrusion of a leucocytosis, brought about by secondary infection, is able to obliterate more or less the specific character of the blood. Such conditions must naturally be considered apart, and should not be used to overthrow the general characteristics of the picture. No one surely would deny the diagnostic value of glycosuria for diabetes, because in conditions of inanition, for instance, the sugar of a diabetic may completely vanish, although the disease continues. And one does not deny the diagnostic value of the splenic tumour in typhoid fever, because the enlargement of the spleen may occasionally subside, under the influence of an intestinal hæmorrhage.