186 WILLIAM F, ALLEN 



ration proved to be very useful and was kept close at hand during 

 all operations. 



The operation for severing the mesencephalic root consisted in 

 first makmg a longitudinal incision through the skin of the head 

 and neck a little to the left of the median line and spreading out 

 the skin laterally. Next the left temporal muscle was severed 

 from its attachment to the sagittal crest, parietal and occipital 

 bones and turned to the left side. A small opening was made 

 through the left parietal with a pair of small bone forceps, ex- 

 tending in width from the median sagittal crest over to the left side 

 about 5 mm., and of sufficient length to expose the left cerebral 

 hemisphere. The line between the left cerebral hemisphere and 

 the cerebellum is indicated by a depression, in which there is a 

 transverse venous sinus of considerable size. If due care has 

 been exercised not to cut the meninges, no hemorrhage will take 

 place up to this point. Should one occur, it can be stopped with 

 a little sterile bone wax. (Shortly before an operation I usually 

 boil a little vaseline and beeswax, of equal proportions, in an 

 aluminum crucible, which makes a very satisfactory wax upon 

 cooling.) The instrument used for making the lesion consisted 

 of a piece of steel shaped up into the form of a chisel, *the two 

 narrow sides of the blade were ground down so that the width of 

 the blade, when placed over a section of the guinea-pig's brain 

 stem in the region of the locus coeruleus, would equal the distance 

 between the median line and the brachium conjunctivum. From 

 the demonstration previously described, the necessary depth re- 

 quired to sever the mesencephalic root was fig-ured out, measured 

 off on the blade of the chisel, and indicated by a notch made with 

 a file. Turning again to the demonstration, it was found that 

 an incision made straight downward between the left cerebral 

 hemisphere and the cerebellum, beginning at the median line, 

 would sever the left mesencephalic root immediately behind the 

 inferior colliculus. Since the transverse sinus is situated in this 

 interval, some of the lesions were made through the cephahc end 

 of the cerebellum directly behind the transverse sinus, and others 

 were made through the caudal end of the left cerebral hemi- 

 sphere, directing the path of the chisel straight downward or 



