462 THE AMERICAN NATURALIST. (VoL. XXXIV. 
worthy that this new departure was initiated to a large extent 
by one of the oldest working neurologists, Kólliker, who, in his 
presidential address, delivered before the Anatomische Gesell- 
schaft at Munich, in May, 1891, pointed out the relative unim- 
portance of the problem of the anatomical origin of nerve 
fibres and raised the really vital question, Is there any nerve 
fibre not directly connected in some part of its course with 
a ganglion cell? To this question Kölliker gave a negative 
reply, and this reply has been confirmed by all subsequent 
investigators. Every nerve fibre, be it of direct or of indirect 
origin, is somewhere in its course directly connected with a 
ganglion cell. In the vast majority of cases the fibres are 
associated each with a single cell and no more; but in some 
instances, as, for example, among the worms, fibres are known 
to be directly connected with several cells. 
Kolliker's generalization contains the germ of the neurone 
theory and leads at once to the statement of that theory as 
made by Waldeyer in an address before the Berliner medi- 
cinische Gesellschaft in June, 1891. This may be stated as 
follows : The nervous system is not correctly described as 
composed of nerve fibres, ganglion cells, and neuropile, but it 
is composed of nervous cells whose bodies we recognize as 
ganglion cells and whose processes are the cores of the nerve 
fibres and the neuropile directly connected with these cells. 
The nervous system then is made up of units, each one of 
which consists of a ganglion cell provided with longer or 
shorter processes, the cores of the nerve fibres, and produ- 
cing from its surface and from that of its fibres fine fibrils, 
which collectively constitute its neuropile and which bring it 
into physiological connection with other such units. To these 
nervous units Waldeyer gave the name * neurones," and the 
belief that neurones are the structural elements of the nervous 
system constitutes the neurone theory. 
It must be plain from what has been said that each neurone 
is nothing more than a modified cell. It is characterized, as 4 
rule, by the possession of only one nucleus, and its most obvi- 
ous peculiarity is that its cytoplasm is in part drawn out into 
very delicate and enormously elongated processes, the cores of 
