32 PRACTICAL PHYSIOLOGY 



(6) The subject fixes his eyes upon a distant object in a good light 

 and then closes them for a few seconds. He now opens them and 

 again looks at the distant object. Watch the pupil carefully the 

 moment the eyes are opened and note whether there is any change. 

 (Light Reflex.) 



Alternatively, in the optical room hold an electric lamp behind 

 the head, then in front of the eyes, and note any change in the pupil. 



(c) (i) Repeat the first experiment (a) but shade one eye with the 

 hand and watch the pupil. 



(ii) Get the subject to close one eye only, observe the other pupil 

 now and also when the eye is opened again. Describe the changes. 

 (Consensual Reflex.) 



3. Skin Reflexes. 



At home test the various skin reflexes described in the Text Books. 

 (Read Reflex Action in Text Book.) 



C. STIMULATION OF NERVE 



These experiments upon Reflex Action show that the nerves to 

 the muscles are generally brought into action, stimulated, by changes 

 at their origins in the spinal cord. 



But they may also be stimulated at any part as is shown by 

 I. 3, p. 31, or by the following experiment. 



Press on your ulnar nerve as it passes behind the internal condyle 

 of the humerus and note the result. To what point is the resulting 

 sensation referred ? 



Lesson VI. To be provided for each pair of Students. 



1. Induction coil, mercury-key and wires, cells or electric supply from 

 accumulator. 2. Frog. 3. Frog-plate on stand. 4. Pins. 5. Small glass 

 of strong acetic acid. 6. Jelly-jar (small) filled with water. 7. Two jelly 

 jars, one with 1 in 1000 sulphuric acid, and the other with 1 in 500 acid. 

 8. Blotting paper. 



For the Class. 



Microscopes with (a) a piece of nerve teased in 0'75 per cent. NaCl ; (b) a 

 transverse section of a nerve ; (c) a transverse section of the spinal cord 

 stained by Weigert-Pal's method. 



LESSON VII 

 D. THE ACTION OF NERVES ON SKELETAL MUSCLE 



Examine with the microscope (1) a piece of frog's muscle teased 

 in 0-75 per cent. NaCl ; (2) a preparation showing the endings of 

 nerve in muscle. 



METHODS. The action of nerve on skeletal muscle may be 

 investigated in two ways (1) by stimulating the nerve, (2) by 

 throwing it out of action. 



Connect up an induction coil for single induced shocks, using 

 the pin electrodes provided (see Appendix, p. 81). 



