122 



COMPARATIVE ELECTRO-PHYSIOLOGY 



of rest ; using a dilute solution, to obtain a positive varia- 

 tion ; and, lastly, applying a dose of intermediate strength, 

 to discover the very interesting case in which the reagent 

 would give rise immediately to a positive variation, and after 

 a longer or shorter continuance of its action, to a reversed, or 

 negative variation, of the current of rest. These inductions 

 are found fully verified in the experiment which I am now 

 about to describe. 



FIG. 86. Action of 7 per cent. Solution 

 of Na 2 CO 3 on Natural Current of Musa 



Preliminary positive variation represented 

 by down curve followed by reversal, 

 50 seconds after application. 



FIG. 87. Effect of CO., on 

 Natural Current of Musa 



Preliminary positive seen to be 

 succeeded by negative variation 

 5 minutes after application. 



Applying a strong solution of sodium carbonate 10 per 

 cent, or above at the electrical contacts on Musa, the result 

 is a negative variation of the natural current. If now a dilute 

 solution of i per cent, be applied on a similar specimen, we 

 obtain a response by positive variation. And if, lastly, we 

 use a 7 per cent, solution, we obtain, as will be seen from the 

 record (fig. 86) the preliminary positive, succeeded, under the 

 continued action of the agent, by reversal to the negative, 

 variation. 



We pass next to the question of the effect of gases. In 

 fig. 87 is given a record of the action of carbonic acid on 



