2^0 Charles G. Rogers. 



N. The Substitution of Another Metal for Sodium. 



Dr. Loeb^ has shown that in the case ot the skeletal muscles 

 which are made to give rhythmic contractions by means of elec- 

 trolytes, it is possible to substitute in the place of the sodium 

 another metal, especially lithium. Up to the present time no one 

 has succeeded in making such a substitution in the case of cardiac 

 muscle. A large number of expermients were made using lithium 

 chloride in the place of sodium chloride in the Van't Hoff solution. 

 In no case was it found that rhythmic contractions would con- 

 tinue in such a solution for a longer time than they would in a 

 pure sugar solution. 



SUMMARY AND CONCLUSIONS. 



1. The blood of the crab studied, Brachynotus nudus, probably 

 has the same concentration as the average of the sea water of the 

 bay. 



2. On account of the fact that the heart does not cease beating 

 when it is removed from the body of the animal it is impossible 

 to determine that any substance is essential for the origination 

 of rhythmic contractions. It has been demonstrated, however, 

 that such contractions will not long continue when NaCl is absent. 

 Calcium, potassium and magnesium each have an important 

 influence upon the heart contraction. 



3. The balance between the salts entering into the composition 

 of the artificial solution, and presumably of the blood also, is a 

 very delicate one and can be determined with great accuracy. 



4. Sodium chloride has the power to restore rhythmic contrac- 

 tions in hearts which have ceased beating in some other solutions. 



5. Hearts which have ceased beating in a pure NaCl solution 

 do not again beat when placed in a solution lacking in NaCl. 



6. The presence of a supply of oxgyen in the solutions is neces- 

 sary for rhythmic contractions. Oxygen may be supplied by 

 adding small amounts of hydrogen peroxide to the solution or by 

 allowing oxygen gas to bubble through it. 



7. The solution most favorable for rhythmic contractions of 

 the crab's heart was found to have the following composition: 



'Loeb, J. Festschrift fiir Professor Kick, 1899. 



