26o DESIGN IN NATURE 



A good example of reflex manifestations as bearing on nutrition is supplied by the vaso-motor system of 

 nerves, which regulates the supply of blood in the smaller arteries by alternately narrowing and widening their calibre. 

 This is effected by acting on the muscular coats of the vessels. If the arteries be greatly narrowed and the quantity 

 of blood passing through them reduced, the organ supplied by them is under-fed : if, on the contrary, the arteries 

 are dilated, and the quantity of blood unduly increased, the organ is over-fed. 



While the vaso-motor system can and does act independently of the brain, it nevertheless is in sympathy with 

 it and can be influenced by it. Thus in the phenomena of blushing and blanching, the skin is alternately made 

 ruddier or paler than natural. Both results are emotional, and are obtained through the instrumentality of the 

 cerebro-spinal nervous system, especially the brain. An unworthy insinuation or indehcate remark frequently raises 

 a blush, and terror or an appalhng piece of intelhgence or shock usually induces pallor. 



There are constrictor and dilator branches of the vaso-motor system of nerves whose function it is to regulate 

 the amount of blood passing through the smaller arteries and the capillary blood-vessels through which the plasma 

 or hquid portion of the blood oozes and feeds the tissues. As the blood moves very slowly in the capillaries, oppor- 

 tunities are afforded for a reverse oozing of effete matters into the capillaries from without. The outgoing (out- 

 flowing nomishing current) and the ingoing (in-flowing waste product current) are osmotic in their nature ; the walls 

 of the capillaries being to all intents and purposes osmotic membranes. 



As there are constrictor and dilator branches of the vaso-motor nerves for regulating the flow of blood in 

 the smaller arteries and capillaries, so there are two sets of nerves, for quickening and slowing the number of the 

 beats made by the heart in a given time. Similarly, there are two sets of nerves for co-ordinating and regulating 

 the movements of the hollow viscera with sphincters, such as the stomach, rectum, bladder, and uterus. These 

 insure that when the body of the viscus contracts or closes, its sphincter simultaneously and spontaneoxisly opens. 

 Conversely, when the sphincter relaxes or opens, the body of the viscus simultaneously contracts or closes. The 

 diametrically opposite movements witnessed in viscera with sphincters are more or less under the control of the 

 reflex nervous system, which, as explained, acts as apart from irritation and stimulation. 



The movements of the viscera in question, though largely, are not wholly, under the influence of the two sets 

 of nerves in question, as the movements, in not a few cases, are more or less voluntary, and, to a certain extent, 

 under the guidance of the brain. They can, under certain circumstances, be temporarily suspended. 



The heart, which is to be regarded as the most important of the hollow viscera, is peculiar in this, that it never 

 ceases to perform its opening and closing rhythmic movements, and it is the rarest thing in the world for any one 

 to be able to stop the beating of the heart for even a few seconds. This dangerous power has been practised 

 in only a very few cases, and once with a fatal result. 



If the heart once stops beating, it is next to impossible to get it to start beating afresh. Failure of the heart's 

 action is the dread of modern society, and the terror of all those who administer chloroform in surgical opera- 

 tions, especially such operations as involve sudden shock to the nervous system — as, for example, the extraction of 

 teeth, toe-nails, &c. 



What is said of the heart is also true of the rhythmic movements of the chest. If the respiration which is 

 unceasing day and night be once fairly suspended, the chances of reviving it are, as a rule, not great. 



In the higher animals, especially man, all the systems are elaborated — division of labour being carried to an 

 extreme. They are also carefully adapted to each other ; they are dependent and interdependent ; they are finely 

 adjusted and balanced ; they are self-acting ; they act separately and in concert. In the normal living individual 

 all the systems must be intact and in perfect working order. This is especially true of the nervous system. As 

 regards normal reflex acts the spinal cord, its nerve centres and nerve cells, its sensory or afferent and its motor or 

 efferent nerves, must all be intact and healthy. Disease or mutilation of any of the parts necessarily vitiates or 

 destroys every form of reflex act. 



Living compound organisms must be regarded as wholes, and any attempt at isolation generally proves abor- 

 tive. The part cannot possibly represent the whole. It is for this reason a mistake to speak of the reflex acts 

 as things per se ; they are simply nerve manifestations of a kind. They are not wholly dissociated from so-called 

 mental acts traceable to changes occurring in the brain. This follows, because they are the product of nerve 

 matter, which is continuous, and which, as regards the brain and cord, differs less in kind than in degree. All the 

 parts of the nervous system run into each other. The cerebro-spinal and sympathetic systems, ganglia, their nerve 

 cells, sensory and motor nerves, &c., form one grand whole. It is not possible to have well-defined Ind entirely 

 isolated nerve function where there is continuity of nerve substance. The vaso-motor nerves, in the phenomena of 

 blushing and blanching, are affected, as stated, by the condition of the brain. Similarly, the action of the heart 

 and the chest movements, are influenced by mental and emotional states. The heart may be pained, and its move- 

 ments quickened or slowed, by cerebral conditions. What is known as " breathless excitement " influences the chest 



