252 Charles G. Rogers. 



EXPLAXATION OF PlATE. 



All records read from right to left. The time marker indicates intervals of thirty seconds. 



Fig. I. .Record of a heart beating in a solution containing 100 cc. f m. NaCl, 2.2 cc. | m. KCl, 

 7.S cc. g m. MgCl2, 3.8 cc. I m. MgS04, i cc. | m. CaC!2, .75 cc. | m. NaHCOs and oxygen. It will be 

 noticed that the first beats were strong, but became rap idiv weaker, then slower, finally ceasing in less 

 than an hour from the beginning of the experiment. The curve is characteristic of all hearts beating in 

 solutions in which the amount of Na is too great, or the Ca too small. 



Fig. 2. Record of a heart beating in a solution similar to that mentioned above, except that 2 cc. 

 t CaClo were employed. This heart beat for a much longer period than that in the previous experiment. 

 Section h of the record was taken two hours from the start a; section c four hours and section d six hours. 



Fig. 3. Record of a heart beating in a solution similar to those used in the above experiments 

 except that it contains a larger amount of CaCls, viz: 3 cc. | m. solution. The beats maintain their first 

 strength and rate of contraction for a long period. Section b is taken four hours from the beginning of 

 the record, section c seven hours, section d eleven hours, section e eighteen hours 3nd section / twenty 

 hours. At the point x in section d a couple of drops of hydrogen peroxide were added to the solution in 

 which the heart was immersed. Its effect is shown in the ensuing stronger and more rapid contractions. 



Fig. 4. Portion of the record made by a heart beating in a solution similar to those above, but con- 

 taining 3.25 cc. i m. CaClo. The beats shown at a are characteristic for hearts beating in such a solution 

 and under ordinary conditions will continue for periods of thirty hours or more. At the point h the 

 solution containing oxygen was replaced by one which had been heated to expel the gases in solution 

 and then cooled to the same temperature as the solution first employed. The effect of the lack of oxygen 

 is shown in the regularly decreasing force of contraction. At c the heart wa.« again placed in the solution 

 containing oxygen, and after a short time regained its former strength and continued beating for a 

 number of hours. This experiment was repeated frequently with similar results. 



