178 OF A NERVOUS SYSTEM. 



posed of numerous distinct parts, each having a 

 separate ofl&ce, injury to one of these, or even to a 

 part of it, would involve the complete loss of the 

 particular faculty of which it was the seat. As it 

 is, even very extensive disease sometimes impairs, 

 and only to some very slight extent, the actions of a 

 number of nervous organs without completely de- 

 stroying the activity of any one. Nerves often reach 

 their ultimate ramifications after pursuing a most 

 circuitous course, so that in many cases a nerve may 

 be divided without sensation being destroyed in the 

 skin to which its peripheral branches are distributed, 

 because this is supplied by nerve twigs, derived from, 

 other trunks tolerably near its central origin or peri- 

 pheral distribution, which reach the same spot after 

 pursuing a less direct, and perhaps much more cir- 

 cuitous course. Plate I. Cases have been recorded by 

 Richet, of La Pitee, Paris, Dr. J. C. Nott, of New York, 

 and Mr. Savory, in which sensibility was preserved 

 in the parts supplied by so large a nerve as the 

 musculo-spiral nerve, after it had been completely 

 divided (New York Medical Journal, June and 

 August, 1868). 



238. Fundamental and essential characters of a 

 nervous system. — In many of the lower animals I 

 have seen very delicate fibres and masses of bioplasm 

 arranged to form an extensive network amongst the 

 tissues, and in some I believe the entii^ " nervous 

 system" consists of such a network extended through 

 all parts of the oi'ganism. In the common starfish 

 and some other members of the Radiata I have seen 

 distinct indications of the existence of a structure 

 such as I have described, and I have no doubt that 

 when our methods of preparation have been still 

 further improved we shall be able to demonstrate the 

 nerve-tissue Avherever it exists, and distinguish it 

 with certainty from the tissues amongst which it is 

 distributed. 



