538 THE OUTGO OF ENERGY 



the blades of which are covered with rubber 

 tubing. 



The force of the individual contractions 

 will be increased but their frequency will be 

 diminished. 



The Influence of Temperature on Frequency of 

 Contraction. Let the drum move at such a 

 speed that the individual heart-beats in the 

 curve shall be close together, but yet separate 

 and distinct. Surround with normal saline solu- 

 tion at 25 C. 



The frequency of contraction will be increased. 



Replace the warm solution with normal saline 

 solution at 5 C. -- . .i.v 



The frequency of contraction will be dimin- 

 ished. 



The Action of Inorganic Salts on Heart Muscle. 

 Sever the apical two-thirds of the ventricle of the 

 tortoise heart from the remainder of the ventricle 

 by a cut parallel with the auriculo-ventricular 

 furrow. With a second parallel cut remove 

 from the severed portion a ring two or three 

 millimetres wide. Divide the ring to form a 

 strip. Fasten one end of the strip to the short 

 limb of a glass rod bent at a right angle. By 

 means of a silk thread connect the .other end of 

 the strip to a heart lever arranged to record the 



