The free nuclei that are observed, whose appearance Pappenheim explains by a preceding solution of the protoplasm (plasmolysis), he regards, in opposition to Rindfleisch and Neumann, not as the beginnings of a developmental series, but as the surviving remnants of the degenerated dying blood cells. Clinical observation, certainly, does not support this conception of Pappenheim's; in as much as in suitable cases with numerous free nuclei (leukaemia, blood crises) transitional forms, which according to Pappenheim must necessarily be present, are not to be found. Moreover, in alluding to a case of leukaemia of this kind, this author himself admits that the appearance of free nuclei can be explained in this instance by the exit of the nucleus. Although Pappenheim, as above mentioned, recognises no difference between megaloblasts and normoblasts in embryonic blood as far as the fate of the nucleus is concerned, he nevertheless decidedly supports Ehrlich's separation of the erythroblasts into these two groups, as two haematogenetically distinct species of cells. He does not regard as distinguishing characteristics, the size and haemoglobin content of the cells--although as we have described above, these are in general different in normo- and megaloblasts--for these two properties undergo such great variations as to increase considerably under certain circumstances the difficulty of diagnosis of individual cells. The chief characteristic is, as Ehrlich has always particularly insisted, the =constitution of the nucleus=. The nuclei of cells which are with certainty to be reckoned among the normoblasts are marked by the absence of structure, their sharply defined contour, their intense affinity for nuclear stains. That is by properties which histology sums up under the name =Pyknosis= (Pfitzner) and recognises as signs of old age. The nuclei of the megaloblasts are round, shew a good deal of structure, and stain far less deeply. [beta]. The clinical differences. Normoblasts are found almost invariably in all severe anaemias that are the result of trauma, inanition or organic disease of some kind. They are however mostly rather scanty, so that a preparation must be searched for some time before an example is found. But occasionally, most often in acute, but also in chronic anaemias, and even in =cachectic= conditions, every field shews one or more normoblasts. V. Noorden was the first to describe a case in which in the course of a haemorrhagic anaemia normoblasts temporarily appeared in such overwhelming numbers in the circulating blood, that the microscopic picture, which at the same time comprised a marked hyperleucocytosis, was almost similar to that of a myelogenous leukaemia. And as in addition to this occurrence the number of blood corpuscles was nearly doubled, v. Noorden gave it the distinctive name "blood crisis." The following procedure is to be recommended for the investigation of the blood crisis: