BY DR. MICHAEL FOSTER. 401 



cannot manifest its irritability because all its branches are 

 poisoned ; the right sciatic can, by means of those brunches 

 which through the ligature have been removed from the in- 

 fluence of the poison-bearing blood. 



With moderate doses of urarij the small branches appear to 

 be poisoned and to have lost their irritability^ while the trunks 

 are still intact. 



O/AS. IV. In a fresh, strong frog, dissect out a gastrocne- 

 mius (or an}' other single muscle), dividing both insertion and 

 origin and ligaturing its bloodvessels, thus leaving it connected 

 with the rest of the body by its nerve only. Poison the frog 

 with urari. 



It will be found that stimulation of the nerve fibres supply- 

 ing the muscle at any part of their course, whether close to 

 the muscle, or in the sciatic trunk as far away as possible from 

 the muscle, will produce contractions in the muscle, though all 

 the other motor nervvi in the body seem to have lost their 

 irritability. 



In a similar way it may be proved that if only the portion 

 of nerve immediately next to the muscle be kept from the in- 

 fluence of the poison, however much the rest may have been 

 subjected to the action of the poison, the muscle may be 

 Sr,thro\vii into contractions by stimuli applied to any part of the 

 ^Hurse of the nerve. The presumption is, that urari acts on 

 The extreme ends only of the nerve, possibly on the end-plates. 



Yet, as we have seen, however much the muscles themselves 

 be exposed to the action of the poison, they do not lose their 

 irritability. These two facts (1), that urari poisons the ex- 

 treme peripheral ends of the nerves, and (2), that the muscles 

 themselves do not under urari lose their irritability, form to- 

 gether a very strong argument for the view that muscles pos- 

 sess an independent irritability of their own. 



Obs. V. Get ready a nerve-muscle preparation. Place one 

 pair of electrodes (A) (as far apart as practicable) on the 

 muscle itself, another (B) on the nerve near the muscle, and a 

 third (non-polarizable) pair (C) on the nerve also, a little 

 higher up than B. Connect A and B with induction coils, 

 and determine the minimum stimulus required to be sent 

 through each pair of electrodes in order to produce a contrac- 

 tion in the muscle. It will be as well to record the contraction 

 by means of the lever, etc. The irritability of the nerve (elec- 

 trodes B) and of the muscle and nerve together (electrodes A) 

 will thus be respectively determined. 



Now pass through C a strong ascending constant current ; 

 and while the current is passing, determine as before the mini- 

 mum .stimulus for A and B. By the ascending constant cur- 

 rent the portion of nerve between the electrodes C and the 

 muscle has been thrown into a state of anelectrotonus ; and it 

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