EFFECT OF IONS UPON TISSUE 563 



rhythmically in a pure NaCl solution, but beats much more 

 rapidly in such a solution than in sea-water, shows that 

 neither the Ca nor K ions of the surrounding medium are 

 directly necessary for the systole or diastole. If they have 

 any effect, they only diminish the rate of contraction (besides 

 maintaining the contractility much longer). But the above- 

 mentioned erroneous conception concerning the role of the 

 three ions can be disproved in another way. .1 had solutions 

 of cane sugar and glycerin prepared which were isosmotic 

 with a -f n NaCl solution. The following solutions were 

 tried : 



(1) 96 c.c. distilled water + 2 c.c. f n KC1 + 2 c.c. Y n CaCl 2 



(2) " cane sugar + " + " " 



(3) " glycerin -f " + " " 



(4) " fwLiCl + " " + " " 



(5) " in NaCl + + 



(6) " fnNaBr + " " + 



In the first four solutions no rhythmical contractions occurred 

 after the first minute. In the fifth and sixth solutions the 

 rhythmical contractions continued for several hours. If it 

 were true that the NaCl serves only to maintain the osmotic 

 pressure, while the Ca produces the contractions, we ought 

 to expect that the Gronionemus would contract just as well in 

 the glycerin or" sugar or LiCl solution as in the NaCl solu- 

 tion. I have made, in addition to these, a number of other 

 experiments, all of which prove that only in solutions of 

 electrolytes (especially Na salts) is the Gonionemus able to 

 contract rhythmically. The belief that calcium is the 

 stimulus that produces the heart-beat is based upon another 

 observation which I think was first made by Howell and his 

 pupils. 1 When a heart stops beating in Ringer's solution 

 it begins to beat again (for a little while) in a solution which 

 contains more Ca. It is easy to confirm this observation for 



i Ibid. 



