iv GENEKAL PHYSIOLOGY OF NEEVOUS SYSTEM 193 



n 



localised to one point of the nerve. Lastly, as was known to 

 the ancients, the simple tying of a nerve prevents physiological 

 conduction along its fibres. 



Fontana (1797) was the first who observed that the gradual 

 compression of a nerve may abolish its conductivity without any 

 concomitant excitatory phenomena. But the subsequent experi- 

 ments of E. H. Weber, Schiff, and others, threw doubt upon his 

 conclusions. They found that the paralysis due to compression of 

 the nerve is preceded by a 

 state of increased excita- 

 bility of the nerve and 

 motor phenomena in the 

 muscle. The subject, which 

 is important to clinical 

 medicine, was methodically 

 investigated by Liideritz 

 (1881), Zederbaum (1883), 

 and Efron (1886), who con- 

 firmed the observations of 

 Schiff. They saw that when 

 the compression of the nerve 

 has not been too severe, nor 

 too prolonged, its conduc- 

 tivity may be gradually re- 

 established. According to 

 Liideritz, gradual compres- 

 sion abolishes conductivity 

 first in motor and later in 

 sensory fibres ; but this 

 observation was contra- 

 dicted by Zederbaum and 

 Efron. In their experi- 

 ments on the nerves of 

 amphibia and of mammals, 

 these authors noted that 

 a pressure of some hundred 

 grammes is always required before conductivity is abolished. 



These experiments were resumed by Ducceschi (1900) 

 Ewald's laboratory by another method, i.e. compression of a very 

 limited area of the nerve by means of a silk thread (about 0'3 

 mm. thick) ; this is passed round the nerve as it lies upon a 

 metal plate through two small holes made in the latter, so that it 

 can be gradually drawn down by a weight (Fig. 126). 



By means of this little apparatus Ducceschi succeeded in 

 diminishing or abolishing conduction in the frog's sciatic by the 

 compression caused by a weight of a few grammes, without any 

 preceding signs of excitation, as already observed by Fontana. 



VOL. Ill O 



FIG. 126. Apparatus for measurable compression of 

 frog's nerve by a silk thread. (Uucceschi.) /, metal 

 plate pierced with two small holes ; n, sciatic nerve ; 

 /, silk thread ; 6, balance to carry weights ; s, support 

 moved by screw v to allow the weight to be applied 

 gradually. 



Ill 



