618 APPENDIX 



HEART BEAT AND BLOOD PRESSURE IN THE TURTLE 



A turtle whose brain has been destroyed and plastron (lower 

 shell) removed, is fastened to a board back down, and with neck 

 extended. The heart can be seen beating through its enclosing 

 membrane, the pericardium. With a fine scissors cut away the 

 pericardium, taking care not to injure the heart. The turtle has 

 two auricles and a single ventricle. Identify these. Determine 

 by careful observation the sequence of beat of the different cham- 

 bers. 



Compare the periods of systole and diastole. 



In the turtle the great veins pulsate as well as do auricles and 

 ventricle. To observe these veins the ventricle must be lifted 

 out of the way. Find the connective tissue frenum which at- 

 taches the tip of the ventricle to the pericardium. Cut this as 

 far from the heart as possible. Seize the frenum with a pair of 

 forceps and by means of it lift the ventricle till the underlying 

 veins can be seen. The beat is seen to originate in these veins 

 whence it sweeps over the heart in the form of a wave. 



Vagus Inhibition. Find the carotid artery where it passes up 

 the neck. Associated with it is a nerve, the vagus. Expose care- 

 fully a short portion of this nerve and stimulate it with repeated 

 induction shocks. In a normal preparation one or the other vagus 

 nerve contains inhibitory fibers whose stimulation will stop tl 

 heart. 



Note whether the standstill occurs in systole or in diastole. 



Graphic Record. Catch a pin-hook either through the frenui 

 or through the very tip of the ventricle. Connect this hook 

 thread or fine wire to the short arm of the heart lever, whicl 

 should be directly above the heart. Obtain on a slowly movii 

 drum a record of the heart beat. While the record is being trac 

 stimulate the vagus nerve. Indicate on the record the period 

 stimulation. 



Determine carefully the interval between the beginning 

 stimulation and the cessation of beat. Note also how long it tak* 

 the heart to recover after cessation of vagus stimulation. 



The Effect of Nicotine. By means of a camel's hair brush apply 

 a few drops of nicotine solution to the surface of the heart. In 

 two minutes repeat the vagus stimulation. The inhibition is 



