458 THE AMERICAN NATURALIST. [VoL. XXXIV. 
tem, it is vastly more characteristic of nervous structures than 
of any other organs in the body. While in most systems dif- 
` ferentiation may be said to have reached the gross organs, in 
the nervous system it has extended beyond this to the cellular 
elements. It follows, therefore, that to know the nervous sys-. 
tem anatomically a study of its gross organs is not sufficient ; 
we must know its cellular composition. Hence it is that our 
more fundamental knowledge of the structure of nervous organs 
is a product of the present century, the century of cellular 
research. 
Although the enunciation of the cell doctrine by Schwann 
in 1839 was accompanied with a remarkably full description of 
the cellular components of most animal tissues, including the 
nervous, it was not until over half a century later that a con- 
sistent cellular analysis of nervous organs was accomplished. 
This was set forth in the conception of the neurone as ad- 
vanced by the Berlin histologist and anatomist Waldeyer in 
1891. The theory of the neurone can best be approached by 
reviewing briefly the historical steps that lead up to it. 
While it is possible that some of the earlier microscopists, 
and particularly the Scotch anatomist Monro, were acquainted 
with nerve fibres, the first unquestionable description of these 
structures was given by Fontana (1781), and Stieda, who has 
reviewed this subject with much care, justly designates this 
Italian physician as the discoverer of nerve fibres. Fontana’s 
discovery, which for some time failed of the recognition that it 
deserved, was eventually confirmed by Treviranus (1816) and par- 
ticularly by Ehrenberg (1833), whose studies showed that the 
central nervous organs, as well as the peripheral nerves, were 
composed of definite fibres. Fontana’s work may be regarded 
as the first step in the modern portrayal of the finer anatomy 
of nervous organs in that it is the earliest unquestionable 
description of nerve fibres. 
Ehrenberg in the narration of his discoveries not only 
described and figured nerve fibres, but he also gave an account 
of other microscopic bodies found in nervous organs, such as 
crystals, blood corpuscles, and certain roundish bodies which 
he called * Kugeln " and which subsequent investigators termed 
