546 STUDIES IN GENERAL PHYSIOLOGY 



occasionally, namely, rhythmical contractions of the muscles 

 of the skeleton. 1 I found that such rhythmical contractions 

 occur only in solutions of electrolytes, i. e., in compounds 

 which are capable of ionizatiou. In solutions of non- 

 conductors (urea, various sugars, and glycerin) these 

 rhythmical contractions are impossible. This is an indica- 

 tion that they are a function of the ion-proteids. But only 

 in certain ion solutions are such rhythmical contractions 

 possible. All the solutions of Na salts are able to produce 

 them, but in a 0.7 per cent. NaCl solution contractions be- 

 gin later and are less powerful than in an equimolecular 

 NaBr solution. This indicates that not only the metal ion 

 influences the physical qualities of the ion-proteids, but that 

 the anion does so as well. This might be understood from 

 the assumption that anions as well as kations may combine 

 with proteids. This forces us to raise the question whether 

 both ions may not combine with the same proteid molecule, 

 only with the difference that the two different ions be added 

 at different places in the molecule. My colleague, Professor 

 Stieglitz, with whom I discussed this question, called my 

 attention to the behavior of amido-acetic acid, which indeed 

 acts in a similar way. From all we know concerning the 

 constitution of proteids it seems justifiable to assume that 

 some of them may very well share certain peculiarities of 

 the amido acids. 2 



The experiments on the rhythmical contractions of the 

 muscles of the skeleton, however, led to some other data 

 concerning the ion proteids. Solutions of Na ions produce 

 rhythmical contractions only if the muscle cells contain Ca 

 ions in sufficient numbers. As soon as there is a lack of Ca 

 ions in the tissues the Na ions are no longer able to cause 

 rhythmical contractions. On the other hand, if we add Ca 



1 Part II, p. 518. 



2 SPIED, Zeitschrifi filr physiologische Chemie, Vol. XXVIII (1899), p. 174 



