DIRECT IRRITATION OF TISSUES. 337 



u o nerves at all are found ; the terminal ramifications of 

 those nearest to it are at best situated in the medulla of 

 the bone immediately adjoining, and that, perhaps, is 

 separated from the irritated spot of the surface by an in- 

 tact, intervening layer of cartilaginous tissue one or two 

 lines in thickness. Now it would indeed be contrary to 

 all experience to conceive that a nerve could from the 

 medulla of the bone exercise a special action upon the 

 cells of the surface of the cartilage, which were the seat 

 of irritation, without a simultaneous affection of the cells 

 lying between the nerve and the irritated spot. If we 

 draw a thread through a cartilage, so that merely a trau- 

 matic irritation is produced, we see that all the cells 

 which lie close to the thread become enlarged through 

 an increased absorption of material. The irritation pro- 

 duced by the thread extends only to a certain distance 

 into the cartilage, whilst the more remote cells remain 

 altogether unaffected. Such observations cannot be ex- 

 plained otherwise than by assuming that the stimulus 

 really acts upon the parts to which it is applied ; it is 

 impossible to conclude that it is conducted to the nerve 

 by any channel perhaps more in accordance with the 

 neuro-pathological doctrine, and then only by reflex 

 action conveyed back again to the parts. 



There certainly are but few tissues in the body which 

 are so completely destitute of nerves as cartilage, but 

 even when we observe what happens in the parts most 

 abundantly supplied with nerves, we find in every case, 

 that the extent of the irritation, or to speak more accu- 

 rately, the extent of the irritated area, by no means cor- 

 responds to the size of any particular nerve-territory, but 

 that in a tissue in other respects normal the size of the 

 affected area essentially corresponds to that of the local 

 irritation. If we make the experiment with the thread, 

 upon the skin, a whole series of nerve-territories are 



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