MUSCLES, NERVES, AND ELECTRICAL ORGANS. 175 



the galvanometer (P) ; 2ndly, the resulting secondary electromotive 

 action shown by the galvanometer ($), and both effects in the 

 ascending as well as in the descending direction of the polarising 

 current. It is a most tedious business to compile such a table. 

 The secondary actions created by the stronger and longer currents 

 are generally so persistent that one almost requires a fresh prepara- 

 tion for each experiment. The only exceptions are the cases where 

 quite weak currents last only for a small fraction of a second, as 

 then the polarisation is transitory enough to allow of other ex- 

 periments, especially with stronger and longer currents to follow 

 them immediately. On the other hand, those cases are also ex- 

 ceptions, in which a current of long duration creates so persistent 

 a polarisation, that the battery-circuit can be opened and the galva- 

 nometer-circuit closed for a short time without perceptibly altering 

 the condition of polarisation. In the other cases where a polarisa- 

 tion, sinking at first rapidly and then slowly, remains behind, it 

 would no doubt be easy to compensate afresh and so produce equi- 

 librium in the galvanometer-circuit. But in repeated experiments 

 in the same preparations one would not be sure of getting the 

 same secondary action as in fresh muscle. If one waits till the 

 polarisation disappears, too much time elapses for it to be assumed 

 that the muscle will behave like a fresh one. On account of the 

 necessity of leaving the pelvis attached to each group 'of muscles, 

 each frog furnishes only one group, so that every experiment which 

 does not come under these two exceptions requires a new frog. 

 But if the results are to be comparable, it is necessary that, firstly, 

 the frogs should not differ too much in size ; and, secondly, that 

 they should be as much as possible in the same condition. If it 

 is remembered that in order to arrive at a fairly complete know- 

 ledge of the phenomena it is necessary to try at least ten times 

 of closure and as many current densities in both directions, which 

 correspond to two hundred experiments ; that these two hundred 

 experiments must be made successively on almost as many frogs, 

 which must be as far as possible equally fresh and large ; and if 

 in addition to this the unavoidable failures and repetitions are taken 

 into consideration, it is seen that a table such as is required is 

 the work of several weeks in which a great number of favourable 

 circumstances must be present, so that no one will be surprised that 

 in so long a time I only attempted it twice. 



The first time, in the autumn of 1 855, I possessed none of the 

 new apparatus or methods of experiment, and I knew as yet 



