246 Charles G. Rogers. 



shown elsewhere to be the "optimum solution" plus hydrogen 

 peroxide or plus gaseous oxygen it would continue to beat for a 

 period ranging from 20 to 30 hours. To show the effect of the 

 oxygen a heart was immersed in such a solution lacking in oxygen. 

 At first the beats were quite strong but became weaker rapidly 

 and within forty minutes had ceased entirely. When the heart 

 had been in the solution for fifty minutes it was immersed in 

 another solution of the same composition but containing hydrogen 

 peroxide. After a latent period of about an hour and a half con- 

 tractions were again resumed, becoming gradually stronger till 

 they had reached a maximum which was steadily maintained. 

 When this heart had been beating steadily for one and three- 

 fourths hours it was again immersed in the solution lacking in 

 oxygen. The contractions were almost immediately slowed and 

 were later reduced in amplitude. After being in this solution for 

 fifteen minutes and the beats had become very feeble the heart 

 was again placed in the solution containing the hydrogen peroxide. 

 After a few minutes of weak contractions it again recovered and 

 continued to give maximum contractions for some hours. The 

 exact length of time during which the beats continued was not 

 taken. 



If instead of adding hydrogen peroxide to the solution we allow 

 a current of gaseous oxygen to bubble through it, taking care that 

 the bubbles do not cause sufficient agitation of the solution to 

 mechanically stimulate the heart to contraction, we find that the 

 heart will make use of the oxygen held in the solution and con- 

 tinue to beat for a long time. (See Fig. 4.) 



K. The Effect of Vant Hoff's Solution. 



Van't Hoff has given us the formula showing the relatne pro- 

 portions of the various salts in the sea water. Calcium is, ac- 

 cording to his statement, the only considerable variant. The 

 other salts exist in the following proportions: NaCl 100, KCl 2.2, 

 MgCl, 7.8, MgSO, 3.8. 



If, as has been supposed, these salts exist in the blood and body 

 liquids of the crab in the same proportions in which they are found 

 in the sea water and the heart of the crab derives its stimulus from 

 such a solution, then an artificial solution containing these salts 



