ture for two or three minutes; mark the minute intervals on the 

 drum immediately helow the writing point. Then replace the solu- 

 tion hy Ringer at a temperature of 10 higher (i.e., 15 ' ), and let 

 the heart record the heats at this temperature, marking the minutes 

 as before. After two or three minutes replace this second solution 

 by a third 10 warmer than the second (i.e., 25 ), and take a simi- 

 lar record at this temperature. Count the number of beats per 

 minute at each temperature. What is the relative increase of rate 

 between 5 and 15? Between 15 and 25? What is the average 

 ''temperature coefficient of acceleration" for a rise of 10 ? How 

 does this compare with the temperature coefficient of chemical 

 reactions ? 



2/7. Actions of salt-solutions on the heart-beat. Take records 

 of the following: Bring the heart, arranged as before, from Ringer's 

 solution ( at room temperature ) into pure m/8 XaCl ; after a 

 minute change this solution for fresh to remove all traces of K 

 and Ca. Note any changes in the rate and character of the beat 

 in this solution. After some minutes change the m/8 NaCl for a 

 mixture of 100 vols. m/8 NaCl -(- 2 vols. m/8 CaCL. Is there 

 any change in the beat? After a few minutes return to pure m/8 

 NaCl and note the effect. Then transfer to a mixture of 100 vols. 

 m/8 NaCl -(- 2 vols. m/8 KC1. Leave in this solution for some five 

 minutes; note any differences from pure m/8 NaCl. Finally return 

 the heart to Ringer's solution. What is the importance of Ca and K 

 for the heart? 



278. Action of C0 2 , acid, alkali, alcohol, and KCN on heart. 

 Using the same arrangement as before, test the action of the fol- 

 lowing solutions on the frog's heart. Take records. 



a. Ringer's solution saturated with carbon-dioxide. The solu- 

 tion should be drawn from the Sparklet siphon bottle shortly be- 

 fore using. 



Try also half-saturated and third-saturated solutions. Return 

 the heart to Ringer's solution soon after definite effects have 

 appeared. 



b. Ringer's solution plus 11/400 HC1. 



c. Ringer's solution plus 11/400 NaOH. 



d. Ringer's solution plus 11/400 KCN. 



e. Ringer's solution plus 4 vol. 7 f etn yl alcohol. 



In all cases determine if the effects produced are reversed by 

 return to normal Ringer's solution. 



Effects of some alkaloids on the heart. Pith a frog or turtle 



