v.] POSITIVE POLARISATION " 89 



you will puzzle the thing out for yourselves. To save space, the 

 formulas, which to show order of individual trials have been set 

 out as above, will sometimes be given thus : 



Frog's skin. Fruit skin. 

 - > ~* *" 



56. Positive polarisation. Let us now turn our attention 

 to another related subject, that of positive polarisation, and of 

 post-anodic (and post-kathodic) action-currents. 



Du Bois-Reymond obtained his first inkling of " positive 

 polarisation" in 1843, but it was not till 1883 that he published 

 a full account of the subject. He introduces that account in 

 the following terms, which clearly indicate the place held by the 

 matter in his thoughts : 



" I consider that the time has come to break the silence which I have 

 preserved till now concerning certain electro-physiological experiments that 

 have engaged my attention for nearly forty years, and to which I attribute 

 very great importance." 



Taking the case of muscle, he studies the secondary polari- 

 sation effects produced by strong constant currents, tabulating 

 his results in relation to current-strength and time of closure ; 

 and how laborious a task this was du Bois' own words will most 

 vividly bring before you. 



"The preparation of such a table of data is a very wearisome under- 

 taking. The secondary effects of currents that are at all strong or long, are 

 for the most part so enduring that a fresh preparation is required for nearly 

 each single experiment . . . each fresh preparation requires a fresh frog 

 . . . to permit of comparison, the frogs must be as uniform as possible in 

 size and health. ... So that the completion of a table of data is the 

 work of many weeks, and it will therefore hardly be matter for surprise that 

 I have only twice accomplished the task, once in the autumn of 1855, once 

 in the summer of 1882." 



Each such table comprised 2OO successful observations, 

 with currents of I Daniel to 40 Groves, and closure times of 

 0.006 sec. to 25 minutes. The polarisation currents were of two 

 kinds : negative, first visible after a current of I Daniel passed 

 for a period of I sec. ; positive, requiring at least 2 Groves 



