246 EXPERIMENTAL PHYSIOLOGY. 



retract strongly so that the laminae of the vertebrae are exposed. 

 Much of this can be done by blunt dissection, which will avoid 

 haemorrhage. Cut the tissues between the spinous processes of the 

 2nd and 3rd lumbar and also between the last lumbar and 1st 

 sacral and amputate at their bases, the spinous processes between 

 the two cuts, using a strong bone forceps. Remove the spinous 

 processes and after bleeding has been controlled by the application 

 of cloths wrung out with hot water proceed to open the spinal canal 

 by cutting through the laminae of the exposed vertebrae with bone 

 forceps, taking care that the point of this instrument does not go 

 deeply into the spinal canal. The spinal cord enclosed in the dura 

 is now exposed, but it is necessary in order to expose the roots 

 properly that the articular processes between neighbouring verte- 

 brae be picked away.* (The so-called hawk's bill bone forceps are 

 useful for this process). 



The posterior root ganglia came into view when the articular 

 processes have been removed. After again stopping haemorrhage, 

 which is likely to be considerable at this stage, the roots are pre- 

 pared for stimulation. 



Lift the posterior root of the 6th nerve carefully on a strabismus 

 hook or small aneurysm needle, and tie a ligature round it as near 

 to the ganglion as possible, cutting the root distal to the ligature. 

 Loosen the leg on the corresponding side and stimulate the central 

 end of the root with a tetanising current, using ordinary electrodes. 

 Note the character of the movements of the leg and watch for any 

 changes in the respirations. 



Ligate and cut the 7th posterior root as near the cord as possi- 

 ble and stimulate the peripheral end. 



What conclusion do you draw from the results of these experi- 

 ments? 



The functions of the anterior roots are then determined by a 

 repetition of the same procedure as for the posterior. It is some- 

 what difficult to prepare these roots for stimulation, and it often 

 assists to pass a tape round the cord, by which it is cautiously pulled 

 up and to one side. Observe carefully any difference in the type 

 of movement which results by stimulating the anterior and posterior 

 roots. 



Draw a diagram showing the functions of the roots. 



*It will be observed that the lower (6th and 7th) lumbar roots are larger than 

 those higher up, the level of the 7th being about on a line with the iliac crests. 



