The author's general aim has been to survey as wide a field of evidence
as possible and this had involved excursions into subjects of which he
has little first hand knowledge. This width of range also has
necessitated a somewhat arbitrary selection of evidence and has
prevented full discussion of any indi- vidual problem. The author trusts
that he has not misrepresented anyone's results or opinions, and if this
has occurred, he can only plead in excuse the peculiar difficulty of
giving a brief and yet accurate account of evidence of such a wide
variety. The diagrams reproduced in the article have all been redrawn
and in many cases the original figures or diagrams have been modified
as, for instance, by recalculating dosage on the logarithmic scale. The
original authors therefore have no direct responsibility for the
diagrams in their present form. The author desires to thank Messrs
Arnold and Co. for permitting the repro- duction of Figs. 9 and 23 from
similar figures which appeared in his book "The Mode of Action of Drugs
on Cells"; portions of other figures from this book also have been
reproduced in modified form. The author also desires to thank Dr. J. M.
ROBSON for help in correction of the proofs. Edinburgh, July, 1937. A.
J. CLARK. Contents. I'age Int.roduction . . . . . . . . . . .