

PHENOMENA OF MUSCLE. 249 



Du Bois-Reymond called the closing time which was necessary 

 with a definite strength of stimulating current and a fresh prepara- 

 tion, in order to obtain polarisation in alternately opposite direc- 

 tions, the ' critical time.' (See No. VI. Sect. 9.) Shorter closing 

 times gave with the same stimulating current positive polarisation, 

 and longer, generally negative. Under special conditions, as when 

 descending currents of 30 to 40 Groves were used, positive polarisa- 

 tion reappeared. After all that has been said, the determination of 

 this ' critical time ' has no great value. In anodic polarisation, how- 

 ever, a critical closing time might be spoken of, inasmuch as with 

 fresh muscle and weak stimulating currents the polarisation is nega- 

 tive with short, positive with longer closing times. Even if it 

 were possible always to produce equal density of current at the 

 anodic spots in a series of experiments on fresh muscles, this 

 ' critical time ' would depend essentially on excitability of the 

 muscle, which varies greatly even in frogs which have been kept 

 under the same conditions. 



I cannot yet speak of a ' critical time ' for kathodic polarisation 

 as I have not yet succeeded in demonstrating positive kathodic 

 polarisation. By applying the electrodes to the sides of the prepara- 

 tion, in which case the stimulating current traverses the fibres 

 transversely or obliquely, I have repeatedly observed diphasic polar- 

 isation, and once indeed positive kathodic polarisation. As, how- 

 ever, with this method of leading in the stimulating current, the 

 greater number of the fibres of the muscle must contain both anodic 

 and kathodic spots in the neighbourhood of the kathode, and as the 

 density of current is not the same in the former as in the ktter, 

 it is not surprising that we get in this case diphasic polarisation. 

 But, on this point, I can at present express no definite opinion, 

 because, as I said, I have seldom employed the lateral method of 

 leading in, which is in general unadapted to the purpose, and 

 therefore I possess no series of experiments as to the polarisation 

 which occurs when this method is employed. The discussion of 

 this question must be the object of special researches on polarisa- 

 tion with transverse and oblique currents. 



Du Bois-Reymond avoided leading in through the natural ends 

 of the muscle, because he feared the secondary resistance pointed out 

 by himself in the thin tendons, considering that as 50 Groves were 

 used, and the closing times amounted to 5 min., this must have 

 been considerable. 



In our experiments, which were made with at the most 



