1. Estimation of the absolute number of red blood corpuscles. 2. Estimation of the proportion of white to red corpuscles. 3. Estimation of the proportion of nucleated red to white corpuscles by means of the quadratic ocular diaphragm (see page 31) in the dry preparation. For instance if we find in a case of anaemia, 3-1/2 millions of red blood corpuscles, the proportion of white to red corpuscles = 1/100 and that of the nucleated red to the white = 1/10, then in 1 cubic millimeter there are 3500 nucleated red corpuscles, that is for 1000 ordinary there is 1 nucleated corpuscle. =Megaloblasts= on the contrary are never found in traumatic anaemias. And in chronic anaemias of the severest degree, the result for example of old syphilis, carcinoma of the stomach and so forth, one looks for them almost always in vain, although they are sometimes to be found in leukaemia. On the contrary, the conditions, apparently much milder, in which from the clinical history, aetiology and general objective symptoms pernicious anaemia is suggested, are almost without exception characterised by the appearance of megaloblasts in the blood. Nevertheless in very late stages of the disease they are always scanty, and a very tedious search through one or more specimens is often required to demonstrate their presence. Hence follows the rule, that the investigation of a case of severe anaemia should never be considered closed, before three or four preparations at least have been minutely searched for megaloblasts under an oil immersion objective.