Öccoiulary Degeneration fulluwing Unilateral Lesions etc. 307 



along the posterior border of the ascending parietal convolution from 

 the supero-mesial border of the hemisphei'e down almost to the fissure 

 of Sylvius. The knife was pushed downwards and forwards into the 

 corona radiata in a slanting- direction, and in this way the whole left 

 motor area was "under-cut". This method of "under-cutting" the motor 

 area, instead of completely extirpating it, was adopted in order to 

 avoid, as far as possible, any serious functional disturbance of the 

 hemisphere, vascular or mechanical, with a view to determine the 

 effects produced upon sensation by a lesion limited to the Rolandic 

 cortex. The operations were conducted with the strictest aseptic and 

 antiseptic precautious, and in every case the wounds healed by first 

 intention. 



The animals were allowed to live for a period ranging from two 

 to five weeks after the operation, during which time the symptoms 

 exhibited by them were carefully observed and recorded. They were 

 then killed by an overdose of chloroform, the brain and spinal cord 

 was removed, and those parts which were to be examined for de- 

 generation were put into Miiller's fluid, the rest being kept in 5"/o formol. 

 In the later cases the whole brain and cord was fixed in formol, but 

 for Marchi's method fixation in formol was found to give results not 

 altogether satisfactory. 



Histological Technique. The method most frequently employed, and 

 finallj^ adopted as better than any other, was that of Marchi slightly 

 modified. After partially hardening the brain or cord in Miiller's fluid 

 or a 2°/q potassium bichromate solution for ten days, it was cut into 

 thin slices — not more than^/^g*^^ or ^/g*^ inch thick — and placed in 

 Marchi's fluid (Miiller's fluid 2 parts, l°/o osmic acid solution 1 part) 

 for other ten days. If large excess is used (not less than twenty 

 times the volume of the tissue) it is not necessary to change the fluid. 

 Ground glass stoppered bottles perfectly air-tight must be employed 

 to prevent evaporation of the osmic acid, and these should be kept in 

 the dark to prevent its decomposition. 



With a view to increase the penetrating power of the osmic acid, 



Orr [2] recommends as a substitute for Marchi's fluid a mixture of 



osmic and acetic acids, and in order to increase its rapidity of action 



20* 



