RECORDING HEART TRACINGS 



67 



starts just to the right of the seam in the drum paper. The 

 time marker can be arranged and the time recorded as the 

 record of the heart beat is taken, or the time record may 

 be put on after the heart tracings are finished if the 

 speed of the drum is approximately constant. This latter 

 procedure is advisable for the first few records. It is also 

 advisable to use a signal magnet in the primary circuit ar- 

 ranged in such a manner that the exact moment and the 



Fig. 63. Arrangement of apparatus for recording frog heart tracings by the sus- 

 pension method. The wires from the signal magnet are connected with the time clock. 



duration of the stimulation may be recorded directly be- 

 neath the writing point of the heart lever. The heart trac- 

 ing should have an amplitude of about one-half to one 

 inch. The drum should have a slow or medium speed. If 

 the Harvard drums are used it is often advisable to clamp 

 a folded piece of paper on to the largest fan to thus fur- 

 ther slow the speed. It may be necessary to put a small 

 weight on to the long end of the heart lever to secure the 

 desired amplitude of movement for the tracing. 



