ELEMENTARY EXPERIMENTAL PHYSIOLOGY 31 



muscles by the glass hook so that the electrodes may be inserted 

 under it. Now bring the electrodes under it and stimulate it. Note 

 the result and draw your conclusions as to 



1st. Where fatigue manifests itself. Is it in the nerve or in the 

 spinal cord ? 



2nd. The action of nerve when stimulated upon skeletal muscle. 



4. Is Reflex Action Dependent on the Spinal Cord? 



Pith the frog by passing a thick pin down the vertebral canal so 

 as to destroy the spinal cord (Fig. 21). 

 Note carefully anything that takes place 

 in the muscles as this is done. Study and 

 describe the frog again as to attitude, FlG . 21. Method of pith- 

 movements, effect of touching and pinch- i ng a Frog, 

 ing. Examine the consistence of the 

 muscles and investigate for reflex acts. 



What is the influence of the spinal cord upon the muscles ? 



II. Reflex Action in Man 

 1. The Knee-jerk. 



One student sits with the right leg crossed on the left, closes his 

 eyes and firmly clasps his hands together. Another student strikes 

 the ligamentum patellae of the right leg with the edge of the ear-piece 

 of a simple stethoscope or with the side of the hand, and observes 

 the contraction of the quadriceps extensor f emoris and the movement 

 of the leg. (Fig. 22). 



FIG. 22. Reflex arc involved in the knee-jerk. 



L., Lumbar. S. t Sacral roots of the spinal nerves. To right a tracing showing short latent 



period of knee-jerk, /., and longer period of ordinary reflex, R. 



(From Noel Paton's Essentials.) 



2. Pupil Reflexes. 



(a) Observe the pupil of your companion while he looks (i) at a 

 distant object, (ii) at a near object. Does any change take place 

 in the size of the pupil ? (Accommodation Reflex.) 



