756 STUDIES IN GENERAL PHYSIOLOGY 



water in the same way as the presence of Ca in the blood 

 seems to prevent our muscles from beating. In order to 

 test this idea, I added to the sea-water various salts which 

 precipitate Ca, e. g., NaF and Na 3 HPO 4 . I found that 

 when a little more of these salts had been added than re- 

 quired to precipitate all the Ca in the sea-water, the center 

 behaved indeed in the same way as if it had been put into a 

 pure NaCl solution. When a little less Na 3 HPO 4 was 

 added, the beats began after a latent period, which varied 

 according to the amount of Na 3 HPO 4 added. Kapid con- 

 tractions began at once when 32 c.c. of a ^ Na 3 HPO 4 

 solution was added to 68 c.c of sea-water. The same result 

 was obtained when 16 c.c. of a normal NaF solution was 

 added to 100 c.c. of sea- water. 



The addition of about 13 c.c. of m sodium-citrate solution 

 to 100 c.c. of sea- water also brought about immediate con- 

 traction of the isolated center. This salt does not bring 

 about a precipitation of Ca in the sea-water or the tissues, 

 but excludes the action of Ca ions in another way. 



I did not succeed in bringing about such results with 

 the addition of Na 3 SO 4 to sea-water. Even the addition of 

 32 c.c of m Na 3 SO 4 to 100 c.c. of sea-water did not give 

 rise to contractions, although the irritability of the center 

 was increased. Experiments with the addition of NaHCO 3 

 remained also negative. But as only a few experiments 

 were made with Na 3 SO 4 and NaCHO 3 , it is possible that a 

 continuation of the work might lead to positive results. 



It is, therefore, obvious that the centers can be caused to 

 beat through a diminution of the amount of Ca they contain, 

 and it may be further argued that the presence of Ca in the 

 sea- water is the cause, or at least one of the causes, that pre- 

 vent the centers from beating in sea-water. 



It should, however, be added that, while a certain diminu- 

 tion of Ca in the center is necessary for the development of 



