Effect of Salts U [you the Invertebrate Heart. 239 



The NaCl solution having the same osmotic pressure contains 

 3.783 per cent of NaCl, or is a solution of about f m. concentra- 

 tion. In bays and in the mouths of rivers the osmotic pressure of 

 the sea water becomes greatly modified. Dr. Loeb^ has shown 

 that animals taken from the waters of San Francisco Bay thrive in 

 solutions with an osmotic pressure approximately equal to that 

 of a I m. NaCl solution. The animals upon w^hich the present 

 work was carried out were collected at a point about three miles 

 north of the Golden Gate where the water sweeps by at both 

 flood and ebb of tide in strong currents. At flood tide the water 

 has nearly the same concentration as the water of the open ocean, 

 but at ebb tide it is much freshened by the water of the Sacra- 

 mento River. 



A series of experiments was made to determine the concentra- 

 tion of a solution of NaCl which would favor the rhythmic con- 

 traction of the heart. For this purpose a | m. NaCl solution 

 was employed and this was diluted with distilled water in varying 

 amounts. It might be expected that the beats, if any at all 

 appeared, would continue longest in that concentration of NaCl 

 which most nearly approaches the normal concentration of the 

 blood of the animal. As a result of a long series of trials it was 

 found that a | m. and a ^-^r m. solution of NaCl acted most 

 favorably. Both of these concentrations were employed in the 

 further work. 



B. Is NaCl Essential for Maintanimg Rhythmic Contractions? 



In considering the question whether any substance is essential 

 for the origination of rhythmic contractions the following con- 

 dition must be kept in mind: In order to demonstrate that a 

 substance is necessary for the origination of rhythmic beats in 

 a muscle we must employ a muscle which does not beat rhythmi- 

 cally when it is removed from the body. Dr. Loeb' has shown 

 that this is true in the case of the center of the bell of the medusa 

 Gonionemus, and was able to demonstrate that NaCl is essential 

 for the origination of rhythmic contractions in this muscle. The 



'Loeb, J. Pfluger's Archiv., vol. xcvii, 1903, p. 394. Also University of California Publications, 

 Physiology, vol. i, No. 7, pp. 55-69. 



'Loeb, J. American lournal of Physiology, vol. iii, 1900, p. 383. 



