Effect of Salts Upon the Invertebrate Heart. 24 1 



added to the solution the beats are of regularly decreasing ampli- 

 tude until finally no contraction is visible. When the oxygen 

 supply is ample it frequently happens that the last beats have 

 perhaps one-third of the amplitude of the normal contraction, 

 but they occur at regularly increasing intervals until they cease 

 altogether. 



In some cases irregularities of beat occur. These may be due 

 to injuries received by the heart when it was removed from the 

 body of the animal or from a deficient supply of oxygen. A very 

 marked effect of the cane sugar is the g-reat increase of muscular 

 tone which occurs in all hearts immersed in such solutions. 



If, as has been held by some, NaCl is the substance which is 

 necessary for the development of rhythmic contractions we should 

 find upon adding NaCl to the sugar solution that the length of 

 time during which a heart will continue to beat will be lengthened 

 as we increase the amount of the salt, up to the limit of the con- 

 centration in which this salt exists in the sea water. In order to 

 test this varying amounts of f m. NaCl were added to a f m. 

 cane sugar solution and it was found that as the proportion of 

 NaCl in the solution increased the hearts beat for a longer 

 time. 



The following examples will illustrate: 



No. 222^25 cc. f m. NaCl plus 75 cc. f m. cane sugar beat for 26 minutes. 

 No. 213 — 50 cc. f m. NaCl plus 50 cc. f m. cane sugar beat for 35 minutes. 

 No. 228 — 75 cc. f m. NaCl plus 25 cc. f m. cane sugar beat for 70 minutes. 



(The above experiments were made without adding any extra 

 oxygen to the solutions.) 



In a pure f m. NaCl solution the hearts beat on the whole 

 longer than in the mixtures of NaCl and cane sugar. 



It now becomes of interest to know whether other substances 

 than the NaCl have the power to aid in the maintenance of 

 rhythmic contractions when added to a solution of cane sugar. 

 On account of the importance of calcium, potassium and magne- 

 sium for marine animals we naturally turned first to these in order 

 to answer the question. Small and varying amounts of the 

 chlorides of these metals were added to solutions of cane sugar 

 and records made of the heart contractions under the influence 

 of these solutions. 



