214 CEREBRAL LOCALIZATION 



nerve. The usual consequence of lymphatic obstruc- 

 tion is produced, namely, oedematous swelling of the 

 area drained. So the optic cup fills up, the disc is 

 obscured by transudate, and the vessels are buried 

 from view in the oedema fluid. All this may be 

 exactly reproduced by intracranial pressure in dogs, 

 and when the pressure is removed, restitution to 

 normal takes place. 



Several methods of raising the intracranial pressure 

 were employed, the best results being obtained by 

 the insertion of sponge-tent material inside the 

 skull. Swelling and oedema of the disc, tortuosity 

 of the veins, and over-distention of the lymph- 

 sheath around the optic nerve were all marked. 

 Relief of the pressure rapidly cured them. 



Although we use the conventional term " neuritis," 

 the histological changes are not those of inflammation. 

 For instance, there is no arterial hyperaemia, and 

 the principal infiltration is with cells of connective 

 tissue origin, not leucocytes. 



Further, it has been stated by many observers, 

 and recently defended, with all his great authority 

 and experience, by Sir Victor Horsley, that the degree 

 of the neuritis in the two eyes is a most reliable 

 guide as to the side of the tumour. It is not so much 

 the amount of swelling that is to be taken into 

 account as the age and extent of the changes. These 

 nearly always commence at the upper nasal quadrant 

 of the disc. Thus, optic neuritis best marked in the 

 right eye is of great value in pointing to a right-sided 

 tumour. The further forward the tumour, the more 

 constant does this rule become. 



