LABORATORY MANUAL OF PHYSIOLOGY. 



VI. IRRITABILITY OF NERVE AND MUSCLE TO 

 VARIUS STIMULI. 



Nerve and muscle tissue have in common the properties of ir- 

 ritability. The muscle has, in addition, the power of contractility. 

 In the following experiments the stimulating agents will be ap- 

 plied to the nerve and the contraction of the muscle will be used as 

 an indicator of the efficacy of the stimulus. The stimulating 

 agents may be grouped as mechanical, thermal, chemical, and 

 electrical. 



1. Mechanical Stimuli. Make a sciatic-gastrocnemius prepa- 

 ration. Place the nerve on a glass plate and keep both muscle and 

 nerve moist with physiological salt solution, (a) Cut the nerve 

 near its origin from the cord with sharp scissors. Does the muscle 

 contract ? Tap the nerve with a scalpel handle. 



(b) Cover the nerve with moistened filter paper, place a thin 

 sheet of cork over this; place a small beaker very carefully on the 

 cork and slowly pour mercury through a glass tube of small calibre 

 into the beaker. Does the muscle contract? Which is the more 

 efficacious, a stimulating force gradually applied or one suddenly 

 applied ? 



2. Thermal Stimuli. Heat a needle or a copper wire in the 

 flame of a Bunsen burner to a red heat. Touch the nerve with it. 

 Result? Will this piece of nerve respond again to stimulation? 

 Explain. 



3. Chemical Stimuli. Make a fresh muscle-nerve preparation. 

 Cut the nerve high up. Place on a glass plate, allowing the end of 

 the nerve to hang over the edge. Use a watch glass or other small 

 vessel for containing the reagents to be used. This is brought up 

 to the nerve until its end dips into the contained reagent. That 

 portion of the nerve used is usually destroyed by the chemical so 

 that it is necessary to cut off the end of the nerve after each test. 

 In this manner, try the effect of the following reagents. 



(a) Concentrated solution of sodium chloride. 



(b) Concentrated solution of sodium or magnesium sulphate. 



