44 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



weakened by Faraday's extra current (cf. Halliburton and McDowall, 

 "Handbook of Physiol.," 19th Ed., p. 27, 1930). 



2. Strength of Stimulus and Height of Contraction. — Make a base line. 

 On a stationary drum record at 5 mm. intervals the height of contraction 

 to stimuli of gradually increasing strength (start with the coils well 

 separated). Use one dry cell. More fibres contract on strong stimula- 

 tion. Define the terms minimal and maximal stimulus (cf. Howell, 

 "Textbook of Physiology," 12th Ed., Fig. 9). Text p. 298. 



ADDUCTOR L0N6U^ 



VASTUS INT. 

 SflRTORIUS 



ADDUCTOR MflSNUS 

 RECTUS INTERN. MINOR 

 RECTUS INTERNUS MA70R 



TIBIOFIBULA 



GASTROCNEMIUS 

 TIBIALIS POSTICUS 



Fig. 3. — Ventral aspect of frog's leg to show position of the sartorius muscle. 



3. Non-electrical Stimuli, (a) Chemical. — On a stationary drum 

 record the contraction produced by placing crystals of NaCl on the nerve 

 resting on a glass slide. Wash off with Ringer. 



(b) Mechanical. — Obtain a contraction by pinching the nerve with 

 forceps. 



(c) Thermal. — Touch the nerve with a heated glass rod and record 

 contraction. Label all records carefully before fixing in shellac. 



4. Irritability and Water Metabolism, (a) Drying. — Set up a nerve- 

 muscle preparation for obtaining records and allow the nerve to dry. 

 Stimulate occasionally to test irritability. As the experiment may last 

 two hours, proceed with the next experiments. Now apply Ringer's 

 solution to the nerve with a fine brush. Does it recover? Label records. 



