384 ELECTROTOXUS. 



made to flow from p f to p, then a a f will be diminished and b b' 

 Increased. 



O/jx. VII. Repeat the observation, placing the galvanometer 

 electrodes, not at the cut ends as before, but on any two 

 points from which a natural current can be obtained. Similar 

 results will be observed. 



AVith most dispositions of the electrodes the natural current 

 is increased in the neighborhood of the positive and diminished 

 in that of the negative pole. The region of the negative pole 

 is said to be thrown into katelectrotonus, that of the positive 

 into aiiclrrlmtnniin. 



n//s. VIII. Having determined the amount of diminution of 

 b b' and the amount of increase of a a' when the polarizing 

 electrode is exactly in the middle line between the other two 

 ptiir, shift the. polarizing electrodes nearer to b b' . Be very 

 careful that the electrodes in their new position are exactly the 

 same distance from each other as before, and that the nerve 

 touches the pings of the electrodes exactly as before, so that 

 the only difference established is that a different part of the 

 nerve is placed between the electrodes. He careful also not to 

 disturb the position of the nerves on the two pair of galvano- 

 meter electrodes. If all has been done properly before the 

 polarizing current is allowed to break into the nerve, the 

 amount of deilection at a a' and l> // should be the same as 

 when the polarizing electrodes were in the middle. Now open 

 the key of the polarizing current and determine the deilection 

 at a "' and b b'. The diminution of deflection at b b' should 

 be greater, and the increase at. a <i f less, than when the polar- 

 izing elect rodes were in the middle. Reverse the direction of 

 the polarizing current. The increase at b b' will be greater, 

 the decrease at a a' less, than when the electrodes were in the 

 middle. 



IX. Shift the electrodes (carefully as before) towards 

 a a' instead of towards b ?/, and repeat as in Obs. VIII. It 

 will be found, as before, that the nearer the galvanometer 

 electrodes are to the polarizing elect rodes, the greater the effect 

 either in way of decrease or increase, as the case may be, of 

 the nat ural current. 



Tin' (unnunt <>f clccfrnfon ic incrcn.<r or decrease is greater 

 l/ir t/rarcr the y^;//</x h'.<t>;l lie tn the ]><>lari : i i></ electrode*. 



alt*. X. Having determined the amount of electrotonus es- 

 tablished by the passage of a current from a single cell, use 

 two cell.-, (keeping everything just the same), and compare the 

 results; then three cells; then four. 



Tin' amounl <>f electrolonic increase or decrease of the 

 natural current increases with an increasing intensity of the 

 polarizing cm-rent. 



Obs. XI. Determine the electrotonic increase and decrease 



