SOME NEW BOOKS. 
INTRODUCTION TO PHYSIOLOGICAL PsyCHoLoay. By Dr. Theodor Ziehen. 
Translated by C. C. Van Liew and Dr. Otto Beyer. 8vo. Pp. 284. London: 
Swan Sonnenschein & Co., 1892. 
THE original German work, of which this is a translation, forms a 
useful introduction to the subject. It is short, it is written vivaciously, 
it is usually clear and well-arranged, always interesting; it is not 
a compilation, but the work of a man who has thought out the whole 
subject for himself. The doctrine is by no means free from exception, 
but it is set forth vigorously and consistently. In the present state of 
the subject, any short book is almost necessarily dogmatic in character. 
Perhaps the few polemical passages were better omitted altogether, 
as likely to create an unfair impression when not supported by proofs. 
Professor Ziehen belongs to the small but able body of German 
psychologists who follow the model of the English psychology of 
association, and seek to improve upon their model. The latter half 
of the book attempts to show how associative processes account for 
the complexity of all mental phenomena above sensation. But the 
chief value of the work lies in the consistent and thoroughgoing 
attempt to exhibit in detail the physiological processes which underlie 
the psychical. Without this procedure, hypothetical as it is at present, 
we are unable to explain mental acts; and at the same time this 
method clears up many difficulties, such as those of unconscious 
mental states. 
Professor Ziehen proceeds upon the hypothesis that ideas are 
deposited in different elements of the cortex from the corres- 
ponding sensations, though he is well aware that another hypothesis 
is possible. Unfortunately, in the very chapter on the association of 
ideas, his usual clearness deserts him. He does not explain clearly 
the relation of association by contiguity to association by similarity, 
and he is confused in dealing with the difficult question of whether 
the first kind of association is simultaneous or successive. This 
chapter is one of the less satisfactory parts of the book. His classifica- 
tion of actions into reflex, automatic (he uses this unhappy word in yet 
another sense) and actions proper, is well worked out, but it presents 
many difficulties. He has to class instincts along with reflex and auto- 
matic acts (¢.c., reflexes modified by intercurrent sensations—why sensa- 
tions?) as purely unconscious. The first half of the book is an 
account of the various sensations, and of generalisations, like 
those of the specific energy of nerves and of Weber’s law. A fuller 
account of colour-blindness and of Hering’s hypothesis would be an 
advantage. The psychophysical methods are treated very inade- 
quately, even making allowance for the difficulty of discussing them in 
a short book; and the treatment of the method of right and wrong cases 
(which the translators, following Professor Ladd, absurdly call the 
method of correct and false (mistaken) cases) is apt to be misleading. 
Still, on the whole, the selection made from the multitude of data 
is a good one for elementary purposes, and the statement is clear, 
