ON THE MAMMALIAN NERVOUS SYSTEM. 



289 



was of sufficient size to embrace in its field a considerable range of the figures of 

 the darkened scale on each side of the shadow of the upright. 



( (tUaicct i, CeU- 

 Ccvnpvns 



Fig. 1. 

 RECORDING CIRCUIT. 



^/ tJ^-icctrcUts . 



CapiUctry 

 Electrometer. 



V.. JT (&quot;lock 



H EXCITING CIRCUIT. 



The arrangement by which either of the above-described instruments could be 

 connected with the experimental circuit, and thus with the particular structure, 

 whether spinal cord or nerve, under investigation, is shown in fig. 1. 



In the above arrangement the method of compensation and the method of 

 connection with the tissues call for a few descriptive details. 



(c.) The compensator was of the pattern used in the Physiological Laboratory, 

 Oxford, and was similar in its general plan to that described by BURPON SANDERSON, 

 as used in his work on the electrical properties of Dioncea.* 



The total amount of wire in the instrument offered a resistance of 10 ohms, of this 

 a portion at one end, 125 centims. in length and of 1 ohm resistance, was exposed and 

 lay tightly stretched upon a boxwood scale. Upon this boxwood bed a heavy block 

 carrying a wire was allowed to slide. The block was furnished with a pointed index, 

 the under surface of which, covered with platinum, formed the sole contact with the 

 wire ; its position was easily read upon the scale beneath it. 



The battery used in the primary circuit of the compensator was the Callaml 

 pattern, which is a Raoult battery without any porous cell. This had been found by 

 one of us to be the simplest and most satisfactory battery for the purpose. As used 

 in the present research, it consisted of a glass jar containing about a litre, into this 



* Phil. Trans., 1882. 



MDCCCXCI. B. 2 P 



