THE DECEREBRATE PREPARATION. 253 



With everything ready to take a graphic record of the move- 

 ments of the left leg, the Sherrington electrodes are connected on 

 both sides, each with a separate inductorium, and the recording 

 drum having been started the left sciatic is stimulated momentarily 

 with a tetanising current of moderate strength. The leg drops into 

 flexion because of reflex inhibition of the postural tonus. Does the 

 leg go back to its extended position when the stimulus is removed? 



A similar stimulus is applied to the right sciatic, when a reflex 

 contraction of the left extensor muscle will occur (crossed extension 

 reflex (see p. 240). 



Finally it can be demonstrated that this reflex contraction is 

 inhibited through stimulation of the contralateral sciatic nerve. 

 To do this the right sciatic is stimulated, and whenever the tracing 

 shows that the left extensor muscles are decidedly contracted, the 

 left sciatic is simultaneously stimulated for a brief period. If the 

 proper strength of stimulus is employed, it will be observed that 

 the extensors relax. These observations should be repeated with 

 stimuli of varying strengths and duration. When the stimulation 

 of the left sciatic is discontinued while still maintaining that of the 

 right the muscle goes back to the contracted state. Draw a dia- 

 gram to show the probable arrangement of the reflex pathways in 

 the spinal cord. 



DECEREBRATE PIGEON. 



Demonstration 18. While under the influence of ether the 

 skull is exposed by a transverse incision of the skin. A piece of 

 bone just large enough to expose the cerebrum is quickly removed 

 by sharp scissors. By means of a glass tube connected with a 

 suction pump*, the cerebrum is sucked up. Great care must be 

 taken to avoid injury to the cerebellum, as there is no tentorium 

 in the pigeon. The advantage of this method of decerebration is 

 that the blood is sucked away, thus allowing a clear view of the 

 field of operation. The cavity is plugged with absorbent cotton, 

 and the skin sewn up. The actual decerebration should take but a 

 few seconds. 



*The tube should be slightly drawn out with an opening 2 or 3 mm. in diameter. 

 This tube is connected by rubber tubing to a filter flask so that the brain tissue 

 will not be drawn into the pump. 



