192 PHYSIOLOGY CHAP. 



In 1885 Golgi wrote at the beginning of his celebrated mono- 

 graph : " As regards the central organs of the nervous system, 

 the main task of modern anatomy must be to answer the 

 most pressing of the problems propounded by physiology." The 

 neurone theory, while it harmonises with the cell theory, un- 

 doubtedly corresponds best with the postulates of physiology, 

 although it is far from solving them all adequately. 



Whatever the final solution of this important controversy 

 as to the structure and mode of activity of the central and 

 peripheral nervous systems, it must be admitted that the wealth 

 of physiological facts that have accumulated in this important 

 field have developed quite independently of the prevailing theories 

 of their exact constitution. If the contents of the present 

 chapter are considered without prejudice and we recommend 

 them more particularly to the attention of histologists, it must 

 be admitted that the physiology of the nervous system is far 

 in advance of its anatomy. 



II. In discussing the general physiology of the skeletal 

 muscles we saw that they are normally thrown into activity 

 by the agency of their nerves alone ; when these are cut, all 

 movement instantly ceases. Nerves are no less excitable than 

 muscles ; but while in muscle active reaction to stimuli, i.e. 

 "excitation," is apparent as contraction or relaxation, the active 

 response of the nerve is not visible, but consists in the simple 

 transmission or conduction of the excitation from the point 

 stimulated to the end-organ. The excitability of nerve is therefore 

 manifested in its conductivity, i.e. its capacity for transmitting 

 the effect of local stimulation at one point along its entire 

 length. The excitatory impulse in muscle is also, as we know, 

 propagated along the muscle fibres by physiological conduction, 

 but conductivity assumes a special development in the nerve, 

 and may be considered as its specific function, depending on 

 the particular differentiation and constitution of its protoplasm. 

 Nerve conduction consists not in the propagation of fluid 

 or gaseous materials, as was formerly supposed, but in the 

 transmission of excitation, that is, of the active state of the nerve 

 substance, the conditions, laws, and characteristics of which we 

 must now investigate. 



The fundamental condition of conductivity in a nerve-fibre 

 is its anatomical continuity and integrity. If after dividing a 

 mixed nerve the two ends are brought into perfect contact, we 

 obtain physical continuity, but not the anatomical continuity 

 which is imperative for conduction ; stimuli applied above the 

 section are not transmitted in an efferent direction to the muscles, 

 nor those sent in below in an afferent direction to the centres. 

 An effect identical with that of section is produced by crushing, 

 cauterisation, scalding, and by the action of certain poisons, 



