68 EXPERIMENTAL PHARMACOLOGY 



When all adjustments are made start the drum and take 

 a "normal'' tracing. When about two inches of this has 

 been recorded then stimulate the vagus nerve and get a 

 record of the normal inhibition. It is important that the 

 electrodes do not rest on the neck or thoracic muscles of 

 the frog, for if such is the case these muscles will contract 

 when the current is turned on and the frog will move thus 

 spoiling the appearance of the tracing. Do not stop the 

 heart longer than is necessary (2 or 3 beats). Then allow 

 the heart to recover (the drum is kept running) from the 

 inhibition and record another two inches of "normal' 

 tracing. Then stimulate the vagus. This gives an oppor- 

 tunity to secure two sets of records. 



Now back the drum aw r ay from the writing lever a little 

 and turn it back to the starting point. Lower the drum 



Fig. 64. Medicine dropper for applying solutions to the heart. 



so that the next round of the tracing will be about one- 

 half inch above the first. Pull the druni forward and 

 start it again and when about one inch of tracing has been 

 recorded then drop on to the heart with a medicine dropper 

 (Fig. 64) five or six drops of a saturated solution of ether in 

 normal salt solution ( solubility ==1 to 9). When the tracing 

 again comes directly over the place where the vagus was 

 stimulated in the lower tracing stimulate the vagus again 

 and determine whether or not the drug has affected the 

 reaction of the heart to the inhibition. Now rapidly drop 

 more ether solution on the heart and repeat the vagus 

 stimulation directly over the second inhibition record in 

 the normal tracing. Keep dropping on the drug and note 

 carefully the effect on the rate and amplitude of the heart. 

 Observe the appearance of the auricles and ventricles. Can 

 you determine in your tracing those portions of the rec- 

 ord made by the sinus, auricular, and ventricular contrac- 



