CHAPTER XXXVIII. 

 THE DECEREBRATE CAT II. 



THE DECEREBRATE PIGEON. 



There are certain fundamental reflex reactions which can be 

 studied only after considerable operative preparation of the animal. 

 One of these is RECIPROCAL INHIBITION which the following experi- 

 ment devised by Sherrington clearly demonstrates. In it reflex 

 inhibition is demonstrated of the plastic tonus of the extensor 

 muscles of the knee in decerebrate rigidity and of the same muscles 

 while actively contracted as a result of reflex stimulation. 



Demonstration 17. 



Whenever bleeding has stopped from the neck stump of a decerebrate pre- 

 paration (cat) this is placed on its back on a well-heated operating table and the 

 hind limbs tied in an extended position. With the left leg well abducted, an 

 incision is made about 5 cm. long down the thigh towards the outer border, and 

 then curved across the thigh towards the inner border. The bluntly V-shaped 

 skin flap is reflected along with the subcutaneous fat towards the median line, 

 so as to expose the femoral artery and vein. About 8 cm. outside the artery 

 will be seen the psoas muscle with the femoral nerve emerging from it. There are 

 three branches of the nerve. Of these the outermost (a small branch) runs to the 

 sartorious muscle and is cut, the middle (a large branch) runs to the quadriceps 

 extensor and is left intact and the innermost (a small branch) is the saphenous 

 nerve, which also is cut. Finally, the psoas muscle is cautiously cut across piece 

 by piece, using small scissors for the purpose. By these operations the flexor 

 muscles of the hip joint are rendered incapable of acting on this joint. The 

 operations are repeated on the right leg. 



The sciatic nerves on both sides must now be exposed, cut low 

 down and the central ends placed in Sherrington's electrodes, the 

 branches of them that run to the hamstring muscles being severed. 

 By this latter operation the knee joint is rendered incapable of 

 active flexion. To accomplish these objects an incision is made 

 down the mid line of the back of the thigh, starting above from a 

 point midway between the tuber ischii and the great trochanter and 

 continuing down to the outer condyle of the femur. From the 



251 



