embryonic mice. He was
able in the first place, like Rindfleisch, to produce the exit of the
nuclei from the cells by the addition of "physiological" salt solution
to fresh blood, and is of the opinion that the exit of the nucleus from
the erythroblasts only takes place artificially.

In embryonic blood the metamorphosis to erythrocytes occurs exclusively
by nuclear destruction and solution within the cell, be it in the case
of megalo- or gigantoblasts or of cells of the size of the normal red
blood corpuscle.

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 l