EXPOSING THE TURTLE S HEART (5 



Now by means of a hand bandage saw (Fig. 104), or with 

 a circular saw on a small motor (Fig. 68), cut out a square 

 opening in the plastron over the heart as shown in Fig. 

 67. With a scalpel handle pry up the square piece of 

 plastron and then carefully strip loose the tissues below 

 the square so as to avoid hemorrhage. There should be 

 practically no bleeding. With scissors cut away the peri- 

 cardium and expose the heart. Familiarize yourself with 

 the anatomy of the turtle's heart (Fig. 69). 



In the side of the neck make a longitudinal incision and 



Circular 

 saw 



Spindle 

 extension 



Fig. 68. Method of sawing out a square in the plastron of a turtle by means of 

 a circular saw (3 inches in diameter) attached to a small (1/10 horse power motor). 



expose the carotid artery, the vagus nerve, and the sym- 

 pathetic nerve (Fig. 70). To identify the vagus nerve place 

 a thread around it loosely, lift up the thread, and with a 

 moderately strong tetanizing current stimulate the nerve. 

 Does the heart stop beating? If not, strengthen the cur- 

 rent. The heart normally should entirely cease to beat 

 when the vagus nerve is stimulated with a sufficiently strong 

 current. 



Arrange the turtle and apparatus to record a heart trac- 

 ing as shown in Fig. 67. It may be desirable to use the 

 signal magnet in the primary current for the induction coil 



