78 EXPERIMENTAL PHYSIOLOGY 



light of a knowledge of the distribution of the nerve fibres in the 

 sartorius. Kuhne showed that the upper 4 to 5 mm. of the 

 sartorius contained no nerve fibres, nor could nerve-endings of any 

 kind be traced in this part. The same holds good for the lower 2 

 to 3 mm. Hence in the first part of the experiment only muscle 

 fibre was being exposed to the glycerine ; and as the muscle did not 

 contract, it follows that muscle fibre is not excitable to glycerine. As 

 soon, however, as the lower part had been cut away, some of the nerve 

 fibres became exposed, and as they are excitable to glycerine the 

 muscle was thrown into a series of irregular twitchings. 



'Experiment 4. — Upon the sartorius of the opposite limb perform an exactly 

 similar experiment, but use a salt solution (0*65 per cent.) containing a drop 

 of ammonia solution. The muscle will be found to be extremely sensitive to 

 this, even the vapour of NH 3 from it being quite sufficient to throw it into 

 tetanus. Nerve, on the other hand, is not excited by it. Prove this by dip- 

 ping the freshly cut end of the sciatic nerve of a gastrocnemius preparation 

 into the solution, taking care that the muscle is thoroughly protected from 

 the vapour by folds of blotting-paper moistened with normal saline solution. 

 It is best, too, to hold the watch-glass of ammonia solution above the level of 

 the muscle, and to lift up the nerve by a fine glass rod bent into the form of a 

 hook, and thus dip the cut end of the nerve into the solution. No contrac- 

 tion of the gastrocnemius residts, but the nerve is not unaffected, for it will be 

 found that the part which has been exposed to the fluid, if tested by electrical 

 stimuli, has been killed. 



Experiment 5. — Xiihne's Curare Experiment. — Pin down two strips of 

 copper foil upon a flat plate of cork with their ends about 4 cm. apart, and join 

 them by a strip of blotting-paper moistened with 0*65 per cent. NaCl solution. 

 Connect the copper strips to the secondary coil of an inductorium arranged for 

 tetanising. Prepare a sartorius and cut it transversely into five pieces of equal 

 length, and arrange these in series upon the strip of moist blotting-paper. 

 Starting with the secondary coil at some distance from the primary, send teta- 

 nising shocks through the preparation, gradually increasing the strength of the 

 stimulation until at last one is found which causes the three middle pieces of 

 the sartorius to contract while the upper and lower ends remain quiescent. 

 Increase the strength of the stimulation still further, when the two terminal 

 pieces are also thrown into contraction. If a curarised sartorius be employed 

 all five pieces go into tetanus at once, viz. when the stronger stimulus which 

 was required to tetanise the two terminal pieces in the first experiment is 

 reached. 



The difference in behaviour of the five pieces is due to the fact 

 that the two ends contain no nerve terminals, while the three 

 centre-pieces do, and as was seen from a previous experiment (ex- 

 periment 2) muscle is less excitable than nerve. 



In addition to these experiments other facts are known tending 

 to show the inherent excitability of muscle. Nerve, for instance, is 

 not excited by stimuli which are arranged at right angles to the 

 direction of the fibres, it being necessary that the stimulus or part of 

 it should pass in the same direction as that of the fibres. Muscle, on 



