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258 DESIGN IN NATURE<br />
unstriped muscles of the body generally (heart,^ blood-vessels, &c.), and also to the glandular organs. Some viscera,<br />
however, such as the heart, lungs, the upper and lower parts of the ahmentary canal, &c., in addition receive branches<br />
such as are not so suppUed being provided by nerves derived originally from<br />
direct from the cerebro-spinal system ;<br />
the cerebro-spinal nerves through their sympathetic plexuses. The unstriped muscles of the viscera and other parts<br />
are also under the influence of fibres derived from the cerebro-spinal nerves.<br />
The account given of the nature and relations of the gangha and nerve fibres of the cerebro-spinal and<br />
sympathetic systems is scarcely less conflicting than that given of the leading divisions of the great nerve centres<br />
themselves.<br />
The sympathetic system structurally consists of meduUated fibres ; the fibres being remarkable for their com-<br />
paratively very small size. They pass by means of the white rami communicantes from certain of the cerebro-spinal<br />
nerves into the cord and ganglia of the sympathetic. The cerebro-spinal system is composed of white and grey<br />
nerve substance in varying proportions.<br />
The trunks of the great sympathetic nerve, as explained, are two in number—one on either side of the vertebral<br />
column. They begin at the base of the skull and terminate at the coccyx. The ganglia composing them are united<br />
by nerve fibres from above downwards, from below upwards, and transversely. They are also united by nerve fdaments<br />
with the spinal nerves and their ganglia. Superiorly, they are connected with nerve plexuses which enter<br />
the cranial cavity.<br />
It may be stated generally that the cerebro-spinal system of nerves, with its appropriate ganglia and nerve<br />
fibres, presides over the striped voluntary muscles and movements of the body, and that the sympathetic system<br />
of nerves, with its well-developed ganglia and nerve plexuses, presides over the unstriped involuntary muscles and<br />
movements. This is true up to a point, for, as explained, the cerebro-spinal and sympathetic systems in<br />
several cases interchange nerve fibres, and both systems supply nerves to the same structures. That the cerebro-<br />
spinal and sympathetic systems of nerves do exercise a regulating power over the striped and unstriped muscles<br />
in the higher animals seems proved by experiment, where the division and stimulation of certain nerves retard or<br />
slow the movements of the organs or the parts to which they are distributed ;<br />
the division and stimulation of other<br />
nerves accelerating or quickening the movements. The retarding or slowing nerves are known as inhibitory nerves,<br />
those which accelerate and quicken as accelerator nerves.<br />
The famous Sir Charles Bell was the first strongly to direct attention to the existence of separate sensory and<br />
motor nerves in animals, and relied for proof on the division and stimulation of the nerves themselves. In this<br />
new departure in 1811^ he was followed by Majeridie ^ in 1822. Other original workers, such as the brothers<br />
Weber, Claude Bernard, Brown-Sequard, and Dr. John Reid, soon enrolled themselves under the new banner. Dr.<br />
John Reid, one of my predecessors in the Chandos Chair of Anatomy and Medicine in the University of St.<br />
Andrews, especially distinguished himself in the new field by a series of papers at once thoughtful and brilhant, the<br />
first of which saw the hght in 1835.*<br />
In dividing and stimulating the nerves in the Uving animal it is important to bear in mind that shock to the<br />
system may largely vitiate the result, and render the experiments more or less futile. This is especially the case<br />
where large nerves or branches of large nerves are divided or mutilated. The rule seems to be that the larger the<br />
nerves experimented with, the less rehable the results. The shock caused by the experiment largely accounts for<br />
what is here stated. Nor must certain fundamental facts be lost sight of. As already explained, plants and the<br />
lowest animals are not provided with a nervous system, yet they perform all the important functions of life in its<br />
absence. As, however, a nervous system in certain living forms is not required, it would be a mistake to attach<br />
too much importance to it when present, and to experiments performed on it.<br />
From the brief account given of the nervous system as a whole, it will readily be inferred that it is no easy<br />
matter to deal satisfactorily and conclusively with the reflex acts in animals.<br />
§52. Nerve Reflexes in Animals - Definitions of Reflex Acts ~ Subjects connected with Reflex<br />
Manifestations, &c.<br />
By reflex acts in the higher animals are generally understood acts performed by a portion of the nervous system<br />
(mamly the spinal cord), plus gangha, sensory, and motor nerves, &c., to the exclusion of the brain. The acts are<br />
said to be involuntary and non-intellectual, and yet, in many cases, purposive. They have for their object the<br />
vohmteiT i.rascL^^*''°"^''<br />
'"' '"''°'""*'"'y "'"'"'''• '^ •'"•"Po^^d of striated muscle. It forms a connecting link between the involuntary and<br />
"Idea of a New Anatomy of the Nervous System," printed privately I<br />
in the year mentioned (1811).<br />
Original experiment by Majendie<br />
^ published in the Jom: de Physiol, in 1822.<br />
"An Experimental Im'estigation into the Functions of tlie Eighth Pair of Nerves, or the Glosso-Pharyngeal, rneumo-trastric<br />
Accessory, lirst published ' m 18.35. For reprint see Reid's collected works, published thirteen years later, namely, in 1848.<br />
nnd SninRl<br />
^