vin CONDUCTIVITY AND EXCITABILITY OF NERVE 61 



lobster, while Fick estimates the rate of transmission in the 

 commissural nerves of Anodonta at 1 cm. per sec. only. Von 

 Uexkiill (16) has recently found values of 400 mm. to 1 m. in 

 the nerves of the mantle of Eledone. 



W. A. Boekelmann (17) has recently made some interesting 

 attempts to estimate the rapidity of conduction in the non- 

 medullated fibrils of the frog's cornea, by determining the interval 

 at which a reflex movement (retractio bulbi) appears after me- 

 chanical or electrical excitation of the centre and periphery of 

 the cornea respectively. The same ratio of values was obtained 

 as for the medullated fibres of the trunk, a fact not without sig- 

 nificance to the question whether the peristaltic movements of 

 smooth muscular organs depend upon nervous conductivity, or 

 upon direct propagation of the stimulus from cell to cell. 



From all these calculations we arrive at the important con- 

 clusion that the excitatory process in nerve is transmitted at a 

 comparatively low rate incomparably less, at all events, than the 

 velocity of light or electricity. If, as cannot be doubted, there 

 is propagation of a material, chemical alteration of the sub- 

 strate (substance of axis-cylinder), the qualitative constitution 

 of the latter cannot fail to affect the process of conduction. 

 And, in fact, the dependence of rate of conductivity upon different 

 physiological conditions in the nerve is well known. Helmholtz, 

 in his investigations on the motor nerves of frogs, observed a 

 marked retardation of conductivity in the nerve, as the effect of 

 cold. Fre'de'ricq and Vandervelde again found that the rapidity 

 of nervous conduction in the lobster depended, to a great extent, 

 upon season and temperature. Nerve in this respect behaves 

 analogously to muscle and all other excitable protoplasm. This 

 correspondence is another proof that the process transmitted in 

 the nerve is really a similar alteration to that in all excitable 

 conducting plasma, i.e. a chemical process associated with metabol- 

 ism. These observations are not unnecessary, in view of certain 

 facts and hypotheses to be considered later. 



Sustained pressure and compression of the nerve may seriously 

 injure conductivity, and it is to be remarked that this seems to 

 occur in a different degree in motor and in sensory fibres 

 Liideritz (18) and some others finding the pressure-effect earlier 

 in the former, Zederbaum (19) and others in the latter. 



The action of ancestlietics upon the conductivity of nerve is 



