CHAPTEE VII 



STRUCTURE AND ORGANISATION OF NERVE 



IN nerve, as in muscle, function and all essentially physiological 

 properties are so bound up with the finer structure of the in- 

 dividual elements that it is desirable to give some account of 

 the latter. We need only consider the conductors, the nerve- 

 fibres, since all existing observations on electrical excitation 

 and electromotive action relate almost entirely to these. The 

 nervous system belongs exclusively to the animal organisa- 

 tion, and indeed to the more highly developed Metazoa only. 

 Plants, unicellular animals, and the lower Metazoa have no 

 nerves, and if in exceptional cases (as in the excitatory move- 

 ments of many plants) there are forms of activity which resemble 

 the vital manifestations of the animal organisation as effected by 

 nerves, it is easy to prove that the resemblance is merely 

 superficial. 



In the animal organism, communication between distant organs 

 or groups of organs is generally effected in two ways : first, by the 

 circulation of the nutritive fluids ; second, by the nervous system. 

 The former may be said to act as the more sluggish transport ; 

 materials prepared or taken up in the organ are carried farther, 

 to be profitably assimilated, or excreted. In opposition to this 

 sluggish medium we have the marvellously rapid communication 

 between remotest parts, which is brought about by the nervous 

 system. The mode of action within the nerves has often been 

 compared to that of the telegraph system, and so long as we bear 

 in mind that what is transmitted in the nerve is not electricity, 

 the comparison is a very fair one. With regard to this last point 

 the most extravagant conceptions prevailed, long before the dis- 

 covery of the fundamental phenomena of electro-physiology, and 



VOL. II I) 



