Effect of Salts Upon the Invertebrate Heart. 247 



in the proportions mentioned should be as favorable for the con- 

 tinuance of rhythmic contractions as the blood itself provided v^e 

 add to it the amount of calcium w^hich is usually found in the sea 

 water in vv^hich the animal occurs. Analyses of the sea water 

 showed that the amount of calcium chloride present in the sea 

 water of San Francisco Bay is about one for every one hundred 

 of sodium chloride. The addition then of a corresponding amount 

 of calcium chloride to the Van't Hoff solution should render that 

 solution favorable for the life of the hearts. A series of experi- 

 ments with solutions containing sodium, potassium and mag- 

 nesium in the proportions stated and with calcium as a variant 

 were made. The amount of calcium chloride used ranged from 

 .5 cc. to 3.25 cc. for every 100 cc. of NaCl of the same molecular 

 concentration (yV m.) As the result of these experiments it 

 seems safe to say that the heart of the crab will continue to beat 

 for a long time only in a solution which contains a greater propor- 

 tion of calcium chloride than the sea water. In the following 

 experiments the sodium chloride, magnesium chloride, magnesium 

 sulphate, and potassium chloride were employed in the propor- 

 tions stated above, the concentration of the solutions being yV m. 

 Various amounts of {'^ m. calcium chloride were added as 

 indicated: 



Exp. 349 — 1.0 cc. CaClo to 100 cc. NaCl, heart beat for 50 minutes. 

 Exp. 384 — 1.5 cc. " " " " " " " 90 minutes. 



Exp. 387 — 2.0 cc. " " " " " " " 6hrs. ormore. 



Exp. 513 — 3.0 cc. " " " " " " " 18 hours. 



Exp. 515— 3.25 cc. " " " " " " " 30 " 



* (See Figs. I, 2 and 3.) 



The above figures do not give an adequate idea of the improve- 

 ment in the action of the hearts caused by the increase in the 

 amount of calcium in the solution. There is a very marked im- 

 provement in the quality of the beats, and the regularity of the 

 contractions in addition to the increase in the length of time during 

 w^hich the contractions may continue as the greater amounts of 

 calcium are added. That a part of the effect of the calcium con- 

 sists in neutralizing the poisonous effect of the KCl in the solution 

 was'shown when the amount of KCl employed was less than that 

 called for by the formula. In such cases the amount of calcium 



