76 EXPERIMENTAL PHARMACOLOGY 



ulate the same nerve again with the same strength of cur- 

 rent and determine whether or not the nervous inhibitory 

 mechanism has been affected by the ether. Is the ampli- 

 tude, the rate, or the tone of the heart affected 1 ? If the 

 tone of the muscle is lowered how will this affect the trac- 

 ing? (After the records are all obtained, draw two or 

 three parallel lines around the drum by rotating it against 

 the writing point of a stationary signal magnet or tam- 

 bour. By comparing the general rise or fall of a whole 

 round of heart beats with this constant line any change in 

 muscular tone will be observed at once.) 



Apply ether solution to the heart rapidly mid at the 

 proper position stimulate the vagus nerve. Take several 

 rounds of the tracings (lowering the drum a suitable dis- 

 tance between each two rounds) and observe the continued 

 action of the drug on the heart. Does the vagus nerve be- 

 come more or less effective in stopping the heart? How 

 do you explain this action? The drum may be stopped for 

 a while at the end of each round if the changes in the heart 

 come on very slowly. 



When the heart has almost stopped, then proceed to rap- 

 idly wash off the ether with warm normal salt solution. 

 See if you can get the heart to recover. How do you ex- 

 plain any peculiar rises and falls in the general contour 

 of your tracings? How can you prevent these in later rec- 

 ords? Were you warned about this before? 



Chloroform. (Action on the Turtle's Heart.) 



2. Eepeat the above experiment on a fresh turtle using 

 a saturated solution of chloroform in tap water saline. 

 Does the chloroform affect the nervous inhibitory apparatus 

 of the heart? What difference do you note between ether 

 and chloroform as regards their cardiac action ? 



