CIRCULATION OF THE BLOOD. 



(a) The different contracting parts (see Fig. 27) and the se- 

 quence of contraction. 



(b) The change in form of the different contracting parts. 



(c) The change in color of the different parts during contrac- 

 tion as compared with relaxation. 



(d) The duration of the systolic period as compared with the 

 diastolic phase. 



(e) The change of position of the heart, as a whole, with each 

 systole. 



(/) Gently grasp the ventricle between the thumb and first 

 finger and note the hardening of the muscle with each systole. 



(g) Now carefully excise the heart, including all its pulsat- 

 ing parts, i.e., the sinus venosus with the large veins which empty 

 into it, and the bulbus arteriosus with pieces of the arteries into 

 which it branches. Place the excised heart in a shallow dish or a 

 watch glass containing o.6-per-cent NaCl solution. Does the heart 

 continue to beat ? Is the normal sequence of contraction of the 

 different parts still continued ? What conclusion can you draw 

 from this observation concerning the dependence of the heart beat 

 upon the central nervous system ? 



Count the number of heart beats per minute and compare with 

 the rate of pulsation before excision. 



(h) Warm the heart above the surrounding room temperature, ^ 

 by holding the containing vessel in the hand. How is the beat 

 affected ? 



Float the watch glass on cold water or set it on some snow. How 

 is the rate of pulsation affected compared with the normal and 

 with that of the warmed heart ? 



(i) Using the same heart or a fresh one if necessary, cut off the 

 sinus from its connection with the auricle. Does the sinus continue 

 to beat ? Do the auricles and the ventricle continue to beat ? If 

 so, is there any difference in rate of pulsation between the different 

 parts? 



(y) Sever the auricles from the ventricle by an incision through 

 the auriculo-ventricular groove. Note results as before. 



[83] 



