62 PRACTICAL PHYSIOLOGY 



2. To Record the Cardiac Cycle. 



Place the cork plate with the frog directly under the heart lever, 

 which should have an angled swinging glass point to decrease 

 friction. Pin the frog firmly on the board by two pins dose to the 

 heart, but not through the vagus nerve, fix the legs also by pins and 

 attach the lever to the apex by means of a small clip, or use the 

 thread already inserted, seeing that the thread is vertical (Fig. 59). 

 Adjust the lever (a) by its height on the stand (b) by the spiral 

 spring, so that each heart beat causes the largest range of movement. 

 Then bring the glass point of the lever lightly against the drum ; 

 start the drum at a slow rate (large spindle to small), and take a 



FIG. 58. Contractions of the frog's heart. 



A = auricular, V = ventricular contraction. The time is marked in seconds. The curve should 

 be read from left to right. (The upstroke indicates contraction.) (L.H.) 



record of several cardiac cycles, watching the heart to see which part 

 of the trace corresponds to auricular and which to ventricular 

 contraction. (If the downstrokes and upstrokes are too close 

 together drive the drum on the fast gear from a small spindle on the 

 shafting to a large one on the drum.) Remove the lever and put a 

 time record in tenths of a second under the trace. Fix the tracing. 

 When fixed determine 



(1) The rate of recurrence of the cardiac cycle, i.e. the rate of the 

 heart ; 



(2) the duration of the ventricular systole ; 



(3) the duration of the auricular systole, if this is marked upon 

 the trace. 



