THE PHYSICAL VEHICLE OF CONSCIOUSNESS

In order to arrive at an adequate understanding of mental processes itrnis necessary to have some idea of the machinery whereby the mind makesrncontact with the body.rnrnThroughout every inch of our organism is a network of specialisedrnfibres whose function it is to carry nervous impulses from the sensernorgans to the central nervous system of brain and spinal cord, and fromrnthence out again to the muscles, glands, and other organs of reaction.rnThe sense organs act as receivers of sensation, the nerve fibresrnas transmitters, the central nervous system as a general telephonernexchange, and the muscles, glands, and organs as the executants of thernimpulses of the mind.rnrnSense organs consist of cells, or sets of cells, specialised for thernreception of particular kinds of impressions. That is to say, if thernparticular kind of stimulus they are fitted to receive is administeredrnto them, a change, probably of a chemical type, takes place in theirrnsubstance, which, it is thought, gives rise to energy of an electricalrnnature, which runs along the nerve fibre as along a wire. At thernpresent moment, however, our knowledge of the nature of the nervousrnimpulse is tentative and hypothetical.rnrnLike all other living tissue, the nervous system is built up ofrnmillions of specialised cells. These cells consist of a main cell bodyrnwith prolongations, usually two in number. One of these has a mass ofrnbranching fibres like the root of a plant, and is called the DENDRON;rnthe other consists of a long thread, the end of which is frayed outrninto strands as the end of a piece of worsted may be unravelled. Thisrnprocess is called the AXON.rnrnThe thread-like branches of the axon of one cell interlace with thesernof the dendron of another cell, and a nervous impulse, running down thernnerve fibres, jumps the gap in the same way as the electric currentrnjumps the space between the terminals of an arc lamp.rnrnIt will readily be seen that these interlacing fibrils, millions inrnnumber, ramifying throughout every portion of the body, form a mostrnwonderful system of communication; the brain and spinal cord acting asrna central telephone exchange.rnrnMuscles are composed of long, spindle-shaped cells which are capablernof contraction. Chemical changes are constantly going on in theirrnsubstance. The blood and lymph which bathe them bring food materialsrnand carry away the waste products of their activity.rnrnThese food substances, which are highly organised chemical compounds,rnare stored in the body of the cell. When a nervous impulse is received,rnthese food globules, as it were, explode; that is to say, they breakrndown into their component chemical parts, and the energy which wentrnto build them up is set free in the process and performs the work forrnwhich the muscle is designed.rnrnThe glands are the chemists of the body, and in the crucibles of theirrnminute cells carry out the wonderful processes of living chemistry uponrnwhich our vital functions are based. The quantity and quality of theirrnoutput is controlled by the nervous system, which acts as regulator ofrnevery process of the body.