THE 
AMERICAN NATURALIST 
Vor. XXXIV. June, 1900. No. 402. 
THE NEURONE THEORY IN THE LIGHT OF 
RECENT DISCOVERIES.! 
G. H. PARKER. 
THE nervous system differs from all other systems of organs 
in that its cellular elements show the highest degree of differ- 
entiation. Thus, in the digestive system, the destruction of a 
few liver cells means only a minute diminution in the amount 
of bile secreted, a loss that can be entirely replaced through 
the slightly increased activity of the remaining cells; and in 
the muscular system the removal of a few muscle fibres from 
a given muscle may be made good physiologically by a minimal 
increment of work from the remaining fibres; but the loss of 
à few or even of a single sensory cell in the retina will produce 
a blind spot in that organ which no amount of activity from 
the adjoining cells, aside from possible regeneration, can ever 
replace. Each sensory cell in the more efficient parts of the 
retina has a. function dependent upon its position and, there- 
fore, different from that of any neighboring cell; and, while 
this may not be absolutely true of all parts of the nervous Sys- 
1 A lecture delivered before the Section of Biology of the New York Academy 
of Sciences, Jan. 29, 1900. 
457 
