510 The American Naturalist. [June, 
(b) Vaso-inhibitory , i, e. vaso-dilators and inhibitors 
of the heart. 
2. Nerves of the visceral muscles. 
(a) Viscero-motor. 
(b) Viscero-inhibitory. 
3. Glandular nerves. 
He found that the " vaso-motor nerves for all parts of the 
body can be traced as bundles of the finest medullated fibres 
in the anterior roots of all the spinal nerves between the lOth 
and 25th, inclusive, along the corresponding ramus visceralis 
(white ramus communicans) to the ganglia of the lateral chain 
(main sympathetic chain) where they become non-medullated 
and are thence distributed to their destination either directly 
or after communication with other ganglia." The viscero- 
motor nerves are also fine medullated fibres which become 
non-medullated in the chain of sympathetic ganglia. As to 
the vaso-inhibitory fibres, these too start from the spinal cord 
as fine medullated fibres, becoming non-medullated in the col- 
lateral or terminal ganglia ; the difference between the vaso- 
motor and vaso-inhibitory fibres lies therefore in the place 
where they lose their medulla, the former becoming non- 
medullated in the proximal ganglia, the latter in the distal 
ganglia. The viscero-inhibitory fibres agree with the vaso 
inhibitory just as the viscero-motor agree with the vaso-motor. 
The conclusion arrived at from this work is that " the vascular 
and visceral muscles are throughout supplied by two kinds of 
nerve fibres of opposite function, the one motor and the other 
inhibitory; and that further these two kinds of nerve 
fibres reach the muscle by separate, distinct anatomical paths, 
the difference of path consisting in a difference of origin from 
the central nervous system combined with the fact that the in- 
hibitory nerves lose their medulla in more distant ganglia than 
the corresponding motor nerves." Moreover, the investigation 
of the course of the efferent nerves led Gaskell to regard the 
sympathetic and homologous ganglia as the motor or efferent 
ganglia of these visceral fibres ; so that instead of the old con- 
ception of two nervous systems which interchange fibres with 
each other, he would substitute the following definition of the 
nerve belonging to a spinal segment — "A spinal nerve 
is composed of anterior and posterior roots both ganglionated, 
the ganglion of the afferent root always being stationary, 
while that of the efferent root is vagrant and has traveled 
away to various distances from the central nervous system," 
