56 HEART OF LOGGERHEAD TURTLE. 



albumen of its own egg, but when it is 41 days old it pulsates from 3 

 to 7 hours in the albumen of its egg, which then sustains it better than 

 can a Ringer's solution, or any solution I could devise. The albu- 

 men contains Na, K, Ca, and Mg. 



Fig. 34. Showing the decline in rate and also the length of time that pulsation 

 endured in the hearts of 10 loggerhead turtle embryos (11 to 14 days old) 

 placed in 0.7 per cent NaCl-j-0. 1 per cent MgCl 2 . The heavy dark line shows 

 the average condition, and the fine full lines show the behavior of individual 

 embryos. The dotted lines cover periods from the last observation to the time 

 when the heart ceased to beat. 



The ' ' all or none ' ' principle in pulsation does not apply to the pul- 

 sation of the heart of the embryo loggerhead turtle, for the ventricle 

 ceases first, then after a long time the auricles cease to pulsate, but 

 the sinus still pulsates. Normally, as is well known, the heart-beat 

 originates in the sinus; then after an interval the auricles respond, 

 and finally the ventricle contracts. After the heart which has been 

 removed from the body has ceased to pulsate, however, we may stim- 



