102 EXPERIMENTAL PHYSIOLOGY. 



To show that reflexes can be inhibited by influences from 

 higher centres, place a crystal of salt on the optic lobes which 

 have been exposed in a live frog by quickly cutting off the anterior 

 portion of the head just behind the tympani with heavy scissors 

 (Fig. 30). Now attempt to elicit reflexes by the methods described 

 above. 



THE FUNCTION OF THE SPINAL NERVE ROOTS. 



Experiment 44. Pith the brain of a large frog and fasten it ventral 

 side down. Slit and evert the skin over the last four vertebrae; 

 remove the muscles from the vertebral arches and then open 

 the spinal canal by means of a strong scissors, keeping them 

 close to the bone. Uncover three or four sets of roots. Pass a 

 silk ligature under a dorsal root as far out as possible. Tie and 

 cut distal to the ligature. Stimulate the central end of the root. 

 Tie a ligature under another dorsal root close to the cord and 

 cut the root central to it. Now stimulate distal to the ligature. 

 In like manner test the function of the ventral roots. In this 

 experiment the unipolar method of stimulation will be found 

 best because of the shortness of the spinal roots. The plate 

 electrode, attached by a wire to the secondary coil is placed 

 in contact with the belly of the frog. The other wire is con- 

 nected with a dissecting needle which then serves as the more 

 active electrode to stimulate the nerve roots. Note the nature 

 of the movements produced in the above experiments and draw 

 a diagram showing the functions of the roots. 



THE FUNCTIONS OF THE CEREBRUM IN THE FROG. 



Interesting observations can be made on a decerebrate frog, 

 but it must be remembered that they do not shed much light on 

 the functions of the cerebrum in the higher mammals because in 

 these the cerebral centres are relatively far more important and 

 participate in many reflex activities in which the spinal cord alone 

 is involved in lower animals. 



Experiment 45. Activities of a Decerebrate Frog. Anaesthe- 

 tize a frog by placing it under a beaker together with a piece 



