62 THE AMERICAN NATURALIST. [Vor. XXXIV. 
of the diffuse nervous network, supposed by Gerlach to be the means 
of communication between the nervous elements, and is followed by 
an account of the discoveries made chiefly by the Golgi and the 
Ehrlich methods, whereby investigators were’ led to abandon Ger- 
lach’s views. By this course the reader is led up to the full state- 
ment of the neurone theory by Waldeyer in 1891. The concluding 
chapter of this section deals with the objections which have been 
raised to the theory since its promulgation. The foundations of the 
theory are fourfold: first, it is a priort probable that the nervous 
system, like other parts of the body, is a cellular system; secondly, 
it is well established that the embryonic nerve cells are as distinct 
from one another in the beginning as any other cells; thirdly, the 
nutrition of the nervous elements, as shown in their degeneration, 
etc., is most readily understood on the grounds of this theory ; and, 
fourthly, the selective staining of elements as seen in Golgi and in 
Ehrlich preparations accords well with this view. The objections 
raised against the theory are regarded by the author as relatively 
slight. The union of nerve cells through their. processes, as seen 
occasionally by observers such as Dogiel, is regarded as no more 
objection to the general theory than Siamese twins are to the idea 
that the human species is made up of separate individuals. The 
results of Apáthy's studies, according to which a network much as 
Gerlach believed in is claimed to exist, are stamped with ‘ Not 
proved"; and the author states that even should they prove true they 
afford no grounds for a serious criticism of the theory. 
The second section deals with the external morphology of the 
neurone. ‘The classification of cell processes into axones and den- 
drites is generally accepted, and only a hint is now and then given 
that the conditions in the lower animals show that this distinction 
is one of a very questionable nature and certainly not fundamental. 
The interrelation of neurones through contact only and the so-called 
* retraction theory," so much in vogue with certain classes of psychol- 
ogists, are put in their true light as a matter of great uncertainty. 
The third section, on the internal morphology of the neurone, is a 
masterful presentation of one of the most confused and intricate 
problems of neurology. The interpretation of conflicting results on 
the basis of differences in methods and the sweeping away of diffi- 
culties arising from a confusion in terminology are admirable features 
of this part of the work. In one respect only is the author less happy 
in his treatment of the subject. He expresses the belief that many 
of the problems of the finer anatomy of nerve cells must wait for 
