210 EXPERIMENTAL PHYSIOLOGY. 



and keeping up its rhythmical beats. If the heart tends 

 to become dry, moisten it with normal saline solution, 

 although normal saline containing a little blood is better. 



(c.) Observe also how during diastole the heart is soft 

 and flaccid, and takes the shape of any surface it may rest 

 on, while during systole when it contracts, it becomes 

 harder, while the apex is raised and erected. 



4. Effect of Heat and Cold on the Excised Heart. 



(a.) Place the watch-glass containing the beating heart 

 on the palm of the hand, and the heart will beat faster ; or 

 place it over a beaker containing warm water, which must 

 not be above 40C. Observe that as the temperature rises, 

 the heart beats faster i.e., there are more beats per minute, 

 also that each single beat is faster. 



(t>. ) Remove the watch-glass from the palm, place it over 

 a beaker containing cold water or ice, when the number 

 of beats will diminish, each beat being executed more slowly 

 and sluggishly. 



5. Section of the Heart. 



(a.) With a sharp pair of scissors divide the ventricle at 

 its upper third just below the auriculo- ventricular groove. 

 Observe that the auricles with the upper third of the 

 ventricle attached to them continue to beat spontaneously, 

 while the lower two-thirds of the ventricle no longer beat 

 spontaneously. If it be pricked with a needle, however, it 

 contracts just as often as it is stimulated mechanically. It 

 responds by a single contraction to a single stimulus, but a 

 single stimulus does not excite a series of rhythmical con- 

 tractions. 



(b.) With a sharp pair of scissors divide the auricles with 

 the attached portion of the ventricle longitudinally. Each 

 half continues to contract spontaneously, although it is 

 possible that the rhythm may not be the same in both. 



6. Movements of the Heart. Expose the heart of a freshly 

 pithed frog as directed in Lesson XLIV., 1, or better still, 



