88 LABOR A TOR Y G UIDE IN PHYSIOLOG Y. 



(5) Carefully excise the heart including the sinus veno- 

 sus and the bases of the posterior and two anterior 

 venae cavae, also the bases of the two aortic trunks. 

 Place the excised heart in a watch glass. Obseive 

 whether the pulsation continues. If so, what is your 

 conclusion regarding the relation of the heart move- 

 ments to the central nervous system? 



(6) If the pulsation continues, note whether the rate 

 of pulsation has been noticeably changed by the ex- 

 cision. 



(7) Bathe the heart with a few drops of normal solution. 

 Hold the watch glass in the palm of the hand and note 

 whether the rate changes. 



(8) Float the watch glass upon ice water and note the 

 results. 



(9) If the heart seems vigorous (otherwise procure a 

 fresh one), carefully sever the sinus venosus with the 

 fine scissors. Does the sinus continue to beat ? Does 

 the heart continue to beat ? Interpretation. 



(10) If the heart beats, sever the auricle from the ven- 

 tricle through the auriculo-ventricular groove. Note 

 results. 



(11) If the auricles beat, divide them. If they con- 

 tinue to beat, do they follow the same rhythm? 



(12) If the ventricle becomes quiescent, stimulate it 

 either mechanically or with a single induction shock. 

 How does it respond to a single stimulus? Continue 

 to subdivide the heart until the parts refuse to respond 

 to stimuli. 



(13) Repeat the experiment and see if the same results 

 are reached on subsequent trials. Note results and 

 give your interpretation. 



