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XXVI 



344. Influence of Veratrine on the Contraction of 

 MuscivE. Destroy the brain of a frog, and inject hypoder- 

 mically four or five drops of a 1% solution of sulphate of 

 Veratria. When the frog is under the influence of the poison, 

 cause a reflex act by mechanically stimulating the skin of the 

 leg. The limbs are extended, and remain so for several 

 seconds, due to the prolonged contraction of the extensors over- 

 coming the flexors and thus causing extension of the legs. 



Arrange the induction machine for single shocks and make 

 and break the primary circuit by means of the key. Short- 

 circuit the secondary. Do not stimulate the muscle often as 

 the veratria effect diminishes with the activity of the muscles. 



Make a nerve-muscle preparation, on cutting the nerve 

 notice the prolonged extension of the legs. 



Arrange the muscle lever to record its movements on a 

 slow moving drum. Take a tracing. Note that the muscle 

 contracts quickly enough, but the contraction is very high 

 compared with that of a non-poisoned muscle, while the muscle 

 relaxes very slowly indeed. The relaxation phase may last 

 several seconds. The tracing may show an uneven curve due 

 to irregular spasms of the muscular fibers. 



Take another tracing with a quick revolving drum, and a 

 curve reaching the whole circumference of the drum may be 

 obtained, or the drum may go around several times before the 

 relaxation is complete. 



Note that if the " veratrized " muscle be made to contract 

 several times the effect passes off — only a simple twitch being 

 obtained — but is re-established after rest. A high temperature 

 also causes it to disappear. 



345. Fatigue of Muscle. Arrange an induction coil 

 for break shocks, /. e., adjust the strength of the stimulus so 

 that only one, the break and not the make, will appear. Pre- 

 pare a nerve-muscle preparation, use a long lever and a weight 

 of 50 grams. Use; a slow revolving drum on which to record 

 the muscle tracings, so slow that the ascent and descent of the 

 lever form merely one line. Break the primary current at 

 regular intervals. 



