No. 402.] THE NEURONE THEORY. 459 
ganglion cells. In 1836 Valentine described these ganglion 
cells with much care, and two years later Remak claimed that 
in the sympathetic nervous organs of vertebrates ganglion cells 
were directly connected with nerve fibres. This proposition 
was supported and broadened by Helmholtz in 1842, who main- 
tained that what Remak had claimed for the vertebrates was 
also true for invertebrates. Seven years later, in 1849, Kol- 
liker in the first volume of his newly established Zeitschrift für 
wissensckaftliche Zoologie pointed out the inconclusiveness of 
the observations of Remak and of Helmholtz. The fibres that 
these authors had described as arising from ganglion cells were 
marked in no way as indubitable nerve fibres. Doubtless they 
were nerve fibres, but the histological knowledge of that day, 
as Kolliker rightly maintained, did not preclude them from 
being fibres of another kind. Kölliker then proceeded to show 
that, in the central nervous organs of vertebrates, ganglion cells 
could be found that were directly connected with fibres pos- 
sessing medullary sheaths. As medullary sheaths are found 
only on nerve fibres, it follows that Kolliker's demonstration 
was the first in which it was shown beyond doubt that nerve 
fibres are directly connected with ganglion cells. The connec- 
tion thus demonstrated made it clear that from this time on 
ganglion cells as well as nerve fibres must be reckoned as essen- 
tial parts of nervous organs. This may be said to be the sec- 
ond step in the development of our ideas on nervous tectonics. 
The third step in this direction was taken by the histologist 
Leydig, who, in describing the finer anatomy of the arthropods 
in 1855, stated that the central nervous organs of the spider 
contained, in addition to ganglion cells and nerve fibres, masses 
of material composed of many very fine interlacing fibrils. The 
minutely granular appearance of this material led Leydig to 
call it * Punktsubstanz,”’ though he did not commit himself to 
the idea that it was granular rather than finely fibrous. In 
1872 Gerlach, by the use of gold chloride, discovered an essen- 
tially similar material in the central nervous organs of verte- 
brates, and, while he assumed for this material a network 
structure rather than a simple interlacing of fibrils, the facts 
that he had at hand were in reality much the same as Leydig 
