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26o DESIGN IN NATURE<br />
A good example of reflex manifestations as bearing on nutrition is supplied by the vaso-motor system of<br />
nerves, which regulates the supply of blood in the smaller arteries by alternately narrowing and widening their calibre.<br />
This is effected by acting on the muscular coats of the vessels. If the arteries be greatly narrowed and the quantity<br />
of blood passing through them reduced, the organ supplied by them is under-fed : if, on the contrary, the arteries<br />
are dilated, and the quantity of blood unduly increased, the organ is over-fed.<br />
While the vaso-motor system can and does act independently of the brain, it nevertheless is in sympathy with<br />
it and can be influenced by it. Thus in the phenomena of blushing and blanching, the skin is alternately made<br />
ruddier or paler than natural. Both results are emotional, and are obtained through the instrumentality of the<br />
cerebro-spinal nervous system, especially the brain. An unworthy insinuation or indehcate remark frequently raises<br />
a blush, and terror or an appalhng piece of intelhgence or shock usually induces pallor.<br />
There are constrictor and dilator branches of the vaso-motor system of nerves whose function it is to regulate<br />
the amount of blood passing through the smaller arteries and the capillary blood-vessels through which the plasma<br />
or hquid portion of the blood oozes and feeds the tissues. As the blood moves very slowly in the capillaries, oppor-<br />
tunities are afforded for a reverse oozing of effete matters into the capillaries from without. The outgoing (out-<br />
flowing nomishing current) and the ingoing (in-flowing waste product current) are osmotic in their nature ;<br />
of the capillaries being to all intents and purposes osmotic membranes.<br />
the walls<br />
As there are constrictor and dilator branches of the vaso-motor nerves for regulating the flow of blood in<br />
the smaller arteries and capillaries, so there are two sets of nerves, for quickening and slowing the number of the<br />
beats made by the heart in a given time. Similarly, there are two sets of nerves for co-ordinating and regulating<br />
the movements of the hollow viscera with sphincters, such as the stomach, rectum, bladder, and uterus. These<br />
insure that when the body of the viscus contracts or closes, its sphincter simultaneously and spontaneoxisly opens.<br />
Conversely, when the sphincter relaxes or opens, the body of the viscus simultaneously contracts or closes. The<br />
diametrically opposite movements witnessed in viscera with sphincters are more or less under the control of the<br />
reflex nervous system, which, as explained, acts as apart from irritation and stimulation.<br />
The movements of the viscera in question, though largely, are not wholly, under the influence of the two sets<br />
of nerves in question, as the movements, in not a few cases, are more or less voluntary, and, to a certain extent,<br />
under the guidance of the brain. They can, under certain circumstances, be temporarily suspended.<br />
The heart, which is to be regarded as the most important of the hollow viscera, is peculiar in this, that it never<br />
ceases to perform its opening and closing rhythmic movements, and it is the rarest thing in the world for any one<br />
to be able to stop the beating of the heart for even a few seconds. This dangerous power has been practised<br />
in only a very few cases, and once with a fatal result.<br />
If the heart once stops beating, it is next to impossible to get it to start beating afresh. Failure of the heart's<br />
action is the dread of modern society, and the terror of all those who administer chloroform in surgical opera-<br />
tions, especially such operations as involve sudden shock to the nervous system — as, for example, the extraction of<br />
teeth, toe-nails, &c.<br />
What is said of the heart is also true of the rhythmic movements of the chest. If the respiration which is<br />
unceasing day and night be once fairly suspended, the chances of reviving it are, as a rule, not great.<br />
In the higher animals, especially man, all the systems are elaborated—division of labour being carried to an<br />
extreme. They are also carefully adapted to each other ; they are dependent and interdependent ; they are finely<br />
adjusted and balanced ; they are self-acting ; they act separately and in concert. In the normal living individual<br />
all the systems must be intact and in perfect working order. This is especially true of the nervous system. As<br />
regards normal reflex acts the spinal cord, its nerve centres and nerve cells, its sensory or afferent and its motor or<br />
efferent nerves, must all be intact and healthy. Disease or mutilation of any of the parts necessarily vitiates or<br />
destroys every form of reflex act.<br />
Living compound organisms must be regarded as wholes, and any attempt at isolation generally proves abor-<br />
tive. The part cannot possibly represent the whole. It is for this reason a mistake to speak of the reflex acts<br />
as things per se ; they are simply nerve manifestations of a kind. They are not wholly dissociated from so-called<br />
mental acts traceable to changes occurring in the brain. This follows, because they are the product of nerve<br />
matter, which is continuous, and which, as regards the brain and cord, differs less in kind than in degree. All the<br />
parts of the nervous system run into each other. The cerebro-spinal and sympathetic systems, ganglia, their nerve<br />
cells, sensory and motor nerves, &c., form one grand whole. It is not possible to have well-defined Ind entirely<br />
isolated nerve function where there is continuity of nerve substance. The vaso-motor nerves, in the phenomena of<br />
blushing and blanching, are affected, as stated, by the condition of the brain. Similarly, the action of the heart<br />
and the chest movements, are influenced by mental and emotional states. The heart may be pained, and its move-<br />
ments quickened or slowed, by cerebral conditions. What is known as " breathless excitement " influences the chest