1222 



first ten, fifteen or twenty contractions this value liad considerably 

 decreased in most cases (experiments 20, 21, 22, 23, 26, 27, 28, 

 32 and 66) viz. to about half its original height, and in some cases 

 (experiments 22, 23, 26) even to 0. Apart from numerous irregula- 

 rities the degree of summation is likewise lowered by further sti- 

 mulations but more slowly than at tlrst; after a continued stimula- 

 tion it became 0, for instance, in experiments 2, 4. 9, 20, 21, 24, 

 25. In 7 cases it became evident that an increased stimulation 

 interval may cause summation again. The interval was lengthened 

 in N». 4 from 0.002" to 0.015" 



„ „ 9 „ 0.004" „ 0.008" 



„ „ 20 ., 0.0025" „ 0.0063" 



„ „ 21 „ 0.004" „ 0.005" 



„ „ 23 ,. 0.003" „ 0.0056" 



„ „ 25 „ D.0033" „ 0.0066" 



., „ 26 „ 0.0033" „ 0.0054". 



On the other hand there are likewise a rather great number of 

 experiments (Nos. 1, 3, 13, 14, 17, 19, 64, 65) in which, mostly 

 only at first, the degree of summation was heightened by stimulation. 

 These changes were, however, as a rule much smaller than those 

 mentioned above, while attempts to retain summation with smaller 

 stimulation-intervals did not succeed. 



It has not come to light, to what cause this instability in the 

 consequences of the fatigue must be attributed. Those curve-series 

 in which the decrease of the contraction-height, in other words the 

 effect of the fatigue is most regular, (experiments 19, 20, 21, 23) 

 likewise present a rather regular decrease of the degree of summa- 

 tion. Irregularities in the change of the contraction-heights mostly 

 coincide with irregularities in the degree of summation. The decrease 

 in the summation is most evident in those experiments in which 

 fatigue considerably lengthened the duration of the contraction whilst 

 its height almost remained the same (experiments 2, 4, 5, 6, 7, 8, 

 10); all these were carried out in March at a rather low temperature. 

 Hence the effect which fatigue may have on the duration of the 

 refractory-stage, is a lengthening one. 



Temperature. 



In the following experiments the muscle was placed in a glass 

 vessel, which in experiments 29 to 33 was filled with 0.7 "/o NaCl- 

 solution, while in experiments 34, 60, 61, 62, 63 it acted as a moist 

 chamber. The muscle was fastened underneath to the short arm of 

 the lever and made equilibrium with a weight of about 5 grammes. 



