524 MUSCLE-NERVE PHYSIOLOGY 



millimeters of length. If the tip of the nerve has ceased to respond, then 

 snip it off with the scissors, and repeat the experiment on the fresh end. 



d. Chemical Stimulation. Many chemical substances when brought in 

 contact with living nerve fiber produce nerve impulses. Try crystals of 

 sodium chloride, magnesium sulphate, dilute ammonia, acetic acid, 10 per 

 cent, nitric acid, i per cent, mercuric chloride. 



Tabulate your observations on all the forms of stimulation used above, 

 by the following outline: 



Kind of stimulation. Effect produced. 



3. Irritability of Muscle. Repeat the experiments in number 2 

 above, applying the stimuli, electricity, etc., directly to the muscle substance, 

 choosing as far as possible portions of muscle which do not exhibit nerve 

 fiber. The muscle will usually respond by a contraction to each of the 

 above forms of stimulation. 



These tests do not fully demonstrate the direct irritability of muscle sub- 

 stance, since in each case it is possible that nerves may have been stimulated. 

 The nerve influences over the muscle can be eliminated by the use of drugs, as 

 will be shown in the next experiment. 



4. Independent Irritability of Muscle. The influence of curara on 

 the muscle-nerve preparation is demonstrated as follows: Ligate one leg of 

 a frog near the thigh to stop the circulation on that side. Now inject 

 under the skin of the back three drops of i per cent, curara, allowing twenty 

 to thirty minutes for absorption. Make the following observations: Place 

 the animal on a glass plate with its back up and dissect out the sciatic nerve 

 in each leg. Use care not to injure in any w r ay the accompanying femoral 

 artery. 



a. Stimulate the muscles of the ligatured leg, also the muscles of the cura- 

 rized leg, both will contract. 



b. Stimulate the sciatic nerve of the ligated leg below the ligature where 

 it has not come in contact with the curara; also the sciatic of the opposite 

 side, which has come in contact with the curara. Stimulation of the first 

 nerve produces contraction of its muscle; of the second nerve does not pro- 

 duce contraction of its muscle. 



From this experiment of Claude Bernard's it is evident that the curara does 

 not destroy the irritability of nerve fiber nor the irritability of the muscle 

 fiber, yet it does destroy the influence of the nerve over the muscle, probably 



