1228 



From this table it appears tliat if the muscle was surrounded 

 for some time by carbonic acid, the degree of summation grew 

 considerably less, and even fell in about half the cases to about 

 (experiments 45, 48, 51, 53, 55, 57, 58 and 59). Lerjgthening of 

 the stimulation-interval often caused the summation to return as in 

 experiments 48, 53, 58, 59. In some cases the degree of summation 

 increased after carbonic acid had been led in for some time, viz. 

 in experiments 46, 47, 52, 54 and 55; this was, however, mostly 

 followed by a decrease. Also in this series of experiments a decrease 

 in the summation, with an eventual necessity to lengthen the stimula- 

 tion-interval, most clearly manifested itself, when the duration of the 

 contraction grew much longer and its height did not decrease much. 



From the foregoing experiments it appears that the refractory 

 stage of the frog's gastrocnemius is lengthened by being cooled 

 down, by carbonic acid and by fatigue, especially in those cases 

 in which under these influences the contraction is protracted. In 

 connection with this, the lengthening of the refractory stage most 

 regularly sets in at refrigeration, whilst fatigue gives the most unstable 

 results. This lengthening takes place in various degrees; mostly the 

 stimulation-interval was at last from two to five times its original 

 length, so that it may be assumed that the refractory stage was 

 likewise changed to about that extent. 



As regards the average length of the refractory stage, the values 

 of the intervals used are of course somewhat greater, because the 

 limit where summation only just takes place had mostly not been 



