176 PHYSIOLOGY CHAP. 



in a rudimentary and ill-defined form: to explain this fact we 

 must assume a common protoplasmic basis for both these 

 elementary functions and those evolved in the more perfect 

 organisms by gradual morphological and functional differentiation 

 into the nervous and muscular systems. 



The organs of the nervous system, of which the general 

 physiology will be considered in this chapter, represent the highest 

 grade of morphological and functional differentiation, both in the 

 ontogenetic development of the individual and in the phylogenetic 

 development of the lowest forms of the animal kingdom. 



I. The nervous system in man and other vertebrates consists 

 of : (a) a compact mass the cerebrospinal axis ; (&) nerves which 

 are given off from this axis the cerebral and spinal nerves and 

 distributed, by successive division, into smaller and smaller bundles 

 and branches, to nearly all the organs and tissues of the body ; 

 (c) a vast number of ganglia or nervous nodes, intercalated along 

 the course of the nerves at greater or less distance from the cerebro- 

 spinal axis, many of which form two lateral chains, and constitute 

 the splanchnic or great sympathetic system. 



To the naked eye the nervous system consists of two dissimilar 

 substances the white matter and the grey matter. Under the 

 microscope both are seen to be made up of fibres and nerve- 

 cells, the fibres predominating in the white matter, the cells in 

 the grey. 



Apart from their minute histological structure, the nerve-cells 

 of the cerebrospinal axis and ganglia have long been regarded as 

 the central, and the nerve-fibres as the peripheral, parts of the 

 system. The cells more particularly serve the storage, elaboration, 

 transformation, and development of the specific energies of the 

 system; the fibres more especially conduct and transmit these 

 energies from the periphery to the centre (centripetal or afferent 

 nerves), and from the centre to the periphery (centrifugal or efferent 

 nerves). The inclination to differentiate between the physiological 

 functions of the ganglion cells and of the nerve fibres, which are 

 filiform processes of the cells, became more definite after the 

 discovery of the telegraph by Morse (1837), which to many minds 

 suggested a parallel between the functions of the nervous system 

 and the telegraphic installation of a State. The cells were com- 

 pared to the telegraph apparatus, the fibres to the conducting 

 wires, the cerebrospinal axis to the great central telegraph station, 

 the conglomerated ganglia of the sympathetic system to the inter- 

 mediate exchanges, the peripheral ganglia to the local offices of 

 country towns and villages. 



But despite the apparent analogy between the two systems, 

 which both consist of distant apparatus brought into direct relation 

 by conducting wires, there are huge internal differences in the 

 nature and function of the elements of which the two systems, 



