THE SPINAL PREPARATION. 257 



electrode on one foot (well moistened with strong saline solution) 

 and connect its wire with one pole of the secondary coil to the other 

 pole of which a fine stigmatic electrode is attached. Clear away any 

 blood clot from the upper end of the cord (using a moistened camel's 

 hair brush) and while holding the neck stump in one hand, stimulate 

 the dorsal columns of the cord, first near the median fissure and 

 then as near as possible to the posterior horn of grey matter. . In 

 the former case it is the homolateral hind limb that flexes, in the 

 latter case, the homolateral fore limb. It may be necessary to 

 repeat the observation several times with varying strengths of 

 stimulation in order to secure definite results. 



5. THE FUNCTIONS OF THE SPINAL ROOTS, by removing the lam- 

 inae and articular processes of the lumbar vertebrae. The procedure 

 for this operation is in general the same as that described for the dog 

 (p. 245) with the difference that the spinous processes of the exposed 

 lumbar vertebrae are not cut at their bases, but the laminae are 

 freely exposed by cutting away the muscles which lie over them. 

 The articular processes are then snipped across and while pulling 

 up the lowermost (7th) spinous process with a strong forceps, the 

 laminae are cut through beginning with the 7th lumbar and working 

 upwards. The ganglia of the posterior roots are brought into view 

 by picking away the stumps of the articular processes. The 7th 

 ganglion lies on a line with the iliac crests. 



Finally it is important to use the decapitate preparation to 

 study the various conditions which control THE ARTERIAL BLOOD 

 PRESSURE. The technique is the same as that already described for 

 the anaesthetized dog (p. 79) only, of course, small cannulae must 

 be used and the pressure established in the tubing which connects 

 cannula to manometer prior to removal of the clip from the artery, 

 must not be more than about 50 mm. Hg. 



There are certain vascular reactions which it is especially 

 valuable to investigate in the decapitate preparation. These are: 



1. The effect of stimulation of the spinal cord on the blood 

 pressure. 



2. The effect of varying amounts of epinephrin injected into the 

 femoral vein. 



3. The effect of pituitary extract similarly injected. 



4. The effect of asphyxia. 



This last group of observations may be done by advanced 

 students. 



