ON THE MAMMALIAN NERVOUS SYSTEM. 283 



of this care is obvious to those who are familiar with the limitation of the fibres in 

 the corona radiata, but we think it well to mention the fact, as a malposition of 2 mm. 

 is sufficient, with the stimulus we employed, to prevent the production of the effect. 



2. Exposure of Peripheral Nerves. 



The great sciatic nerve was usually selected for this purpose, and was exposed in 

 the thigh for 6 centims. of its length. It was then divided near the knee, and its 

 central end ligatured, care being taken to prevent any pull upon the structure, or any 

 injury to the arteria comes nervi ischiadici which was always included in the ligature. 

 When not required for purposes of immediate experiment it was irrigated with O G per 

 cent, saline solution, and covered over by the skin and muscular flaps. During use, 

 whether for purposes of excitation or in connection with the non-polarisable electrodes, 

 it was always so fixed that no movement of the animal could pull upon the structure. 



3. Preparation of the Spinal Cord for Observation. 



The spinal cord afforded naturally more difficulty in its preparation, and this 

 requires therefore a more detailed description. 



The objects in view were 



(a.) To expose and divide the cord. 



(&.) To preserve as far as possible its circulation. 



(c.) To fix the spinal column so that no accidental movements of the animal should 

 affect it. 



(d.) To avoid the depression due to cooling, drying, &c. 



(e.) To secure for the purposes of electrical investigation as complete an isolation as 

 possible of its different parts. 



These requirements were met as follows : 



(a.) Exposure and Division. The muscles were rapidly exposed over the dorso- 

 lumbar region, and then partially extirpated and cleared from the vertebral laminae ; 

 haemorrhage was treated by frequent irrigation with O G per cent, saline at a tempera 

 ture of 50 C., and pressure of hot sponges. The exposed vertebral arches were then 

 carefully removed piecemeal for 6 to 8 centims., by the aid of powerful but fine- 

 pointed bone forceps. 



In those cases in which the reflex effects of the lower fragment of cord were inves 

 tigated, the cord was only exposed for a very short distance by the removal of one 

 lamina and then divided under profound anaesthesia. The small wound was then 

 closed and kept covered with hot sponges. 



When a long portion of the cord was exposed the theca was divided in the middle 

 line with great care, the division being especially free at that portion of the exposed 

 area which was to remain in continuity with an unexposed region, so as to avoid 



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