96 ELECTRO-PHYSIOLOGY CHAP. 



tract of the nerve by treatment with amyl alcohol, and compared 

 its local capacity of response with excitability at two other points 

 of the nerve, above and below, excitability diminishes in the first 

 place more rapidly than conductivity, since (as in Griinhagen's 

 experiment with local C0 9 narcosis) the excitability of the injured 

 point is considerably reduced, at a time when it still appears to 

 be unaltered at the upper point. At a later stage, on the other 

 hand, there is an opposite reaction : conductivity is totally 

 abolished, while local excitability persists in a low degree. 



IV. EXCITABILITY IN DIFFERENT NERVES 



All these facts regarding excitability of nerve-fibre relate to 

 the usual frog's nerve-muscle preparation, i.e. gastrocnernius muscle 

 and sciatic nerve. If we take the whole limb, and test the 

 reaction of the other muscles supplied by the same nerve, with 

 different strengths of current, the same intensity of stimulus does 

 not throw all the muscles simultaneously into excitation ; on the 

 contrary, weak stimuli applied in the leg of the frog to the 

 common nerve -trunk produce movement in one functionally 

 co-ordinated group of muscles, i.e. the more excitable, while 

 stronger excitation causes movement of another functionally com- 

 bined, but less excitable, group of muscles. The first set comprise 

 the flexors, as was pointed out by Bitter at the beginning of the 

 century, the second the extensors. His often confused remarks, 

 which are interwoven with the mystical speculations of the natural 

 philosopher, culminate in the notion of an excitability "limited, 

 conditioned, and finite " of the flexors, " unlimited, unconditioned, 

 absolute " of the extensors. Kitter's conclusions have been 

 frequently contradicted, amongst others by du Bois-Eeymond, who 

 refers to them in his great work as highly improbable, urging that 

 they should be rejected until fresh and unimpeachable experiments 

 should be forthcoming. 



This task was undertaken in 1874 by Eollett (49), who 

 rescued the investigations of Eitter from oblivion, and confirmed 

 them by numerous experiments. He did not, like Eitter, employ 

 the constant current, but a rapid succession of tetanising induction 

 currents. With these it is easy to ascertain that minimal stimuli 

 first send those muscles into tetanus which move the foot 

 and tendon forwards and upwards, and also abduct the toes 



