lo in his book on the oxygen requirements of the organism. A few
years ago, Unna, whose notice Ehrlich's remark had no doubt escaped,
described an analogous condition as follows: "in some nodules the mast
cells appeared in part twice as large as usual, especially with the new
mast cell stain (polychrome methylene blue, glycerine ether mixture).
This was caused by the staining of a large round halo, in the centre of
which lay the peculiar long-known mast cell, consisting of blue nucleus,
and an areola of deep red granules. Higher magnification shewed that the
halo was not granular, but very finely reticular; although it exhibited
exactly the same red colour as the granules. It was consequently a
spongioplasm peculiar to these mast cells."

The appearance of the mast cells described by Unna may also be
artificially produced, by allowing a preparation that is stained with
the oxygen containing analogue of thionin, oxamine, to remain for some
time in laevulose syrup or watery glycerine. Evidently part of the dyed
mast cell substance is dissolved and retained in the immediate
neighbourhood. But as Unna possesses great experience of the mast cells
and is a complete master of the methods of their demonstration, one must
suppose that the halos described by him were preformed, and did not
arise during the preparation of the specimen.

It must hence be concluded that an analogous process may go on during
life, that these halos are the expression of a vital secretion of the
substance of the mast cells externally[24].

A condition that Prus has brought forward in the so-called purpura of
the horse, is also to be interpreted as a secretory process of the mast
cells. He describes young mast cells from the haemorrhagic foci of the
wall of the gut, on the margins of which bodies of various sizes
appeared, and which differ essentially from the mast cells themselves by
their staining. Nevertheless from their whole configuration and position
it is evident that these bodies have arisen in the mast cells
themselves; and Prus comes to the conclusion "=that the degenerating
young mast cells secrete a fluid or semi-fluid substance, which as a
rule sets on the surface of the cells, but also, more rarely, in their
interior=."

Evidence that the substance of the granules is given off externally may
sometimes be seen in the polynuclear neutrophil or their analogues. Thus
in rabbit's blood in which he had experimentally produced leucocytosis,
H