MORE than a decade has passed since the first
edition of this book was published. This new
edition follows the same general plan as before,
but nearly the whole of it has been re-written
with a good deal of expansion and modernization.
The account of the structure of cells given in the
first chapter has been profoundly changed as
a result of recent discoveries, and I hope it
may prove useful to many who do not want to
study the rest of the book in detail. Embed-
ding has been much more fully treated than in
the first edition and a section on celloidin
added.

Although this book deals only with one kind
of cytological technique, yet it bears on other
kinds. It is concerned with structure, yet pro-
vides a basis for histochemical studies; it is
cytological, but adapted to the needs of the
histologist and pathologist; it deals with Meta-
zoan cells, but can be used by the protozoologist
and botanist. It contains a good deal of informa-
tion that has not been published previously.

I am very much indebted to friends who have
given valuable advice about this new edition,
especially Dr. W. Holmes, Mr. P. B. Medawar and
Mr. G. M. J. Schmidt, who have shown me errors
in what I wrote before and have generously gone
to a lot of trouble to answer questions on difficult
points. (No error in this edition is attributable
to them, for they have not seen the manuscript.)
I thank Professor E. S. Goodrich once more. All

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