Effect of Salts Upon the Invertebrate Heart. 249 



artificial solution we should have a solution which would be 

 equally as good as the artificial solution in its action upon the 

 heart of the crab. This was indeed found to be the case. The 

 heart beats became more regular and the length of time during 

 which the heart would continue to beat was much increased. The 

 solution now proved to be in every particular the equivalent of 

 the artificial solution. This suggests the possibility that the con- 

 centration of the CaCl, in the blood of the crab, and also the 

 concentration of this same salt necessary for long continued heart 

 action is higher than that of the sea water. 



M. The Role of Sodium Bicarbonate and Sodium Hydrate in 



Artificial Solutions. 



It was found during the course of the experiments that the addi- 

 tion of small amounts of sodium bicarbonate to the solutions em- 

 ployed had a very beneficial effect upon the action of the hearts. 

 For a time it was thought that this substance was in itself a neces- 

 sary component of the liquids intended to favor rhythmic activity. 

 Dr. Loeb^ has shown that the sea water is practically neutral in 

 reaction. How the bicarbonate could affect the action of the 

 heart was a puzzle until it was remembered that very small 

 amounts of free acids in artificial solutions may exert very in- 

 jurious effects. The role of the bicarbonate in neutralizing any 

 free acid that may be present in the solutions throws a new light 

 upon the subject and makes its presence desirable. It has the 

 power to neutralize acids and yet is not itself alkaline in reaction. 

 It is therefore possible to have solutions containing an excess of 

 this substance without affecting the neutrality of the solution. 

 By thus neutralizing any free acid which may be present we 

 make the conditions most favorable for heart activity, and add 

 for the proof of the fact that the body liquids are neutral in 

 reaction. 



The addition of small amounts of j\ NaOH will have exactly 

 the same effect. Care has, of course, to be taken not to add too 

 much of this substance as the solution must not be too alkaline 

 in reaction. 



'Loeb, J. Archiv. fiir die gessammte Physiologic, Bd. 99, 1903, p. 637. 



