HEART OF TURTLE. 



57 



ulatethe ventricle by an induction current, and after the current has 

 been removed the heart may pulsate for several minutes in a reverse 

 manner, each contraction originating at the stimulated place in the ven- 

 tricle, then after a pause the auricles, and finally the sinus contracting. 



60 



50 



20 



3O 



MINUTES 



60 



Fig. 35. The full heavy line shows the average rate and duration of pulsation of 

 the hearts of 10 loggerhead turtle embryos (11 to 14 days old) in 0.7 per cent 

 NaCl. The dotted line shows the same things for the hearts of 10 embryos in 

 0.7 per cent NaCl+0. 1 per cent MgCl 2 . It appears that the NaCl+ MgCl 2 does 

 not affect the rate, but nevertheless it stops the heart sooner than does the pure 

 NaCl solution. 



The heart of the loggerhead turtle often revives temporarily im- 

 mediately before it ceases to pulsate in solutions. This is seen in 

 figures 34 and 36, which show the decrease in the rates of pulsation of 

 the hearts of 20 loggerhead turtle embryos n to 14 days old. Ten of 

 these (fig. 36) were placed in 0.7 per cent NaCl, and 10 others 

 whose pulsation is shown in figure 34 were placed in 0.7 per cent 

 NaCl+o.i per cent MgCl 2 . The MgCl 2 has no effect upon the rate, 

 but it stops the heart sooner than does the pure NaCl. (See fig. 35-) 



After the heart of the loggerhead turtle has ceased to pulsate m 

 NaCl it may be revived temporarily by CaCl 2 . KC1 will also revive 



