The contrary assertions that neutrophil and
eosinophil, or eosinophil and mast cell granulations occur in the same
cell Ehrlich regards as unfounded, from extensive researches specially
directed to this point. Nor has Ehrlich seen a pseudoeosinophil cell of
the rabbit change to a true eosinophil[23]. That such a transition does
not occur is most distinctly shewn by the fact that the various
granulations behave entirely differently towards solvents. With the aid
of acids, for example, the pseudoeosinophil granules can be completely
extracted from the cells, whilst the eosinophil granules remain whole
under this process, and can now be stained by themselves.

The clearest proof that the neutrophil, eosinophil, and mast cells are
entirely separated from one another by the fundamental diversity of
their protoplasm, of which the granulation is but a specially striking
expression, is afforded by the study of the various forms of
leucocytosis. As will be shewn in detail in the following chapter,
neutrophil and eosinophil leucocytes behave quite differently in their
susceptibility to chemiotactic stimulation. Substances strongly
positively or negatively chemiotactic for one cell group are as a rule
indifferent for the other; frequently indeed there is an exactly opposed
relationship, inasmuch as substances which attract the one kind repel
the other. Still greater is the difference between the mast cells and
the other two cell groups; for so far as present investigations go, they
are quite uninfluenced by substances chemiotactic for the neutrophil or
eosinophil cells.

As specific cellular secretions, various kinds of granules must also be
sharply marked off from each other by their chemical properties. The
granules of the blood corpuscles seem to be of very simple chemical
constitution. We have special grounds for the assumption that the
crystalline granulations are for the most part composed of a single
chemical compound, not necessarily highly complex even, but which seems
to be a relatively simple body such as guanin, fat, melanin, etc.
Doubtless other granulations have a more complicated constitution, and
very often are a mixture of various chemical substances. The most
complicated granules of the blood are the eosinophil, which are, as has
elsewhere already been mentioned, of a more complex histological
structure. For a peripheral layer is plainly distinguishable from the
central part of the granule. It should be mention