iv GENEKAL PHYSIOLOGY OF NEKVOUS SYSTEM 195 



stimuli were employed, owing probably to their different intensity. 

 When excitation from chemical stimuli (glycerol or hypertonic 

 salt solution) was no longer able to pass the compressed point, 

 excitation from mechanical stimuli was able to get through ; when 

 the latter was blocked by the compression, electrical stimuli were 

 still effective (Fig. 129). It is an interesting fact that reflex 

 spinal excitation is arrested by a minimal degree of compression 

 such as blocks the transmission of chemical stimuli. 



A frog's nerve ceases to conduct when its diameter is reduced 

 to one-third or one-fourth of the normal ; it then becomes trans- 

 parent, as the fluid contained in the myelin sheath is pushed back 

 above and below the point of compression. Histological inspection 

 of the nerve compressed by a silk thread shows that there is 

 no blackening of the myelin 

 sheath by osmic acid near the 

 point of compression, but the 

 axis-cylinder (the conducting 

 element) is reduced in size. 



After Ducceschi,Signorina 

 Calugareanu (1901) experi- 

 mented iu Dastre's laboratory, 

 by a- somewhat different 

 method, on the effects of 

 mechanical compression of 

 the nerve of the electrical 



Organ Of Torpedo, the frog's FIG. 129. The very rapid contractions at the begin- 



j ,1 LU'.L' ning of the tracing were due to chemical stimula- 



SCiatlC, and the rabbit S VagUS. tion with glycerol, applied to the upper part of 



She also Obtained diminution the nerve. At ^ the nerve was compressed by 



of conductivity without any SSS^^fflSSt?!"? the point 



previous rise of excitability, 



and found that the injurious influence of compression was 



not manifested immediately, but after a certain time (about 1 



minute). 



Bethe, too (1903), studied the effect of compression on frog's 

 nerve by a method similar to that of Ducceschi, with reference 

 more particularly to the histological changes. He found that by 

 a degree of compression which did not abolish conductivity to 

 electrical stimuli the axis-cylinder may be considerably reduced 

 in diameter, at the cost not of the neuro-fibrils which compose it, 

 but of the perifibrillar substance (or neuroplasru). According to his 

 calculations the amount of perifibrillar substance in the normal 

 fibre is to that of a compressed fibre which is still capable of con- 

 ducting, as 654 : 1. This, he says, proves that conductivity is a 

 function of the neuro-fibrils and not of the perifibrillar substance. 

 Bethe further noted that when the nerve-fibres are rendered 

 incapable of conducting by compression, they also lose their 

 capacity for primary staining, i.e. staining with basic dyes in the 



