ey reach the
blood by entirely different ways than the polynuclears do.

We believe that these non-granulated mononuclear cells of man
are to be regarded as analogous to those of the guinea-pig
described by Kurloff (see page 86). The mononuclear cells of
man however are finally transformed into the neutrophil
granulated cells, whilst the cells of Kurloff remain free from
granules in the course of their metamorphosis. In acute
leucocytosis in the guinea-pig only the pseudo-eosinophil
polynuclear cells are increased, which wander as such out of
the bone-marrow, but not the polynucleated non-granulated
forms, which but slowly grow to maturity in the blood. Thus the
peculiarities of guinea-pig's blood, in which two kinds of
polynuclear cells are recognisable, throw light upon the
corresponding conditions in human blood. The distinction in the
latter is more difficult, since it is not evident in this case
that the fully formed polynuclear neutrophil leucocytes have a
twofold origin: for the majority wander fully formed from the
bone-marrow into the blood, and only a considerably smaller
number grow to maturity within the blood-stream from the
mononuclear and transitional forms.

No definite statement can as yet be made as to the places of formation
of the non-granulated large mononuclear leucocytes.

Kurloff has demonstrated, that in the guinea-pig these cells are present
both in the bone-marrow and in the spleen, but that after extirpation of
the spleen the absolute number does not change. The bone-marrow then in
the guinea-pig can also preserve the balance of the large mononuclear,
non-granular cells in the blood.

The numbers we found in our blood investigations in man after
splenectomy were also normal. We may then doubtless assume that the
large mononuclear granuleless cells of human blood also arise for the
most part from the bone-marrow. In this tissue they are to be picked out
in the medley of the different kinds of cells only with the utmost
difficulty, owing to their small number and their but little
characteristic properties. Consequently an exact investigation of their
origin could probably only be successful if it were possible
experimentally to produce a disease in which these forms in particular
underwent important increase. This advance is not quite hopeless, since
in man at least an absolute increase of the la