520 STUDIES IN GENERAL PHYSIOLOGY 
The contractions of a heart preparation fed by an alkaline salt 
solution are much more regular and even than the contractions of 
a sartorius preparation; it is to be particularly emphasized that in 
the first case all the muscle fibers contract evenly and simultane- 
ously, while, as has been pointed out above, in asartorius immersed 
in a salt solution it is the rule that the primitive fibers never con- 
tract simultaneously and equally strongly; much oftener the con- 
tractions observed are local, and the rhythm of the various local 
contractions may vary most decidedly.! 
This difference between the periodic contractions of the 
muscle and those of the heart holds also in the experiments 
which I give below. I do not believe, however, that we can 
conclude from these differences that there are differences in 
the manner in which the rhythmical activities in the two 
cases originate. We cannot, for example, conclude from this 
that the difference is determined through the influence of 
the ganglion cells in the heart. I believe that we deal, 
partly at least, with a difference in conductivity. In the heart 
muscle the stimulus can pass from element to element. If, 
therefore, only one element is stimulated and caused to con- 
tract, the whole heart must become active. In skeletal 
muscle the sarcolemma prevents such a passage of the stimulus 
from element to element, and we obtain in consequence irregu- 
lar isolated contractions of the individual fibers. The case is 
similar to that observed in Medusw, in which we find a syn- 
chronous activity of all the elements when the continuity of 
the elements is complete, and a loss in synchrony when the 
conductivity between the elements is diminished.” 
3. We will now return to our main problem, and endeavor 
to answer the question whether only certain ions are able to 
bring about rhythmical contractions in muscle. 
I tested first of all Biedermann’s assertion that these 
1 BIEDERMANN, loc. cit. 
2Engelmann and Romanes have pointed out this fact. A discussion of this sub- 
ject is found in my Comparative Physiology of the Brain (New York: Putnam's 
Sons, 1900). 
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