SAMUEL ERNEST POND 813 



In running sea water the rate of beat of the excised heart may 

 differ from that observed in the body before the operation. After 

 transfer to the paraffin trough used in the tests the rate of beat at 

 first decreases, or the heart may stop beating altogether. In the 

 latter case hearts usually resume beating in a few minutes after slight 

 pinching or tapping. The rate of beat was always found to increase 

 during the next 10 minutes, and, after this interval it usually remained 

 essentially unchanged. In some cases a decrease in the rate of beat 

 was observed, and the ampHtude of the contraction decreased, al- 

 though the excised heart will frequently beat for 2 days or more. 

 If now, after 30 minutes in sea water, the heart is placed in pure 

 isotonic sugar solution, the beat at first slightly increases in rate and 

 then diminishes through a period of 70 to 80 minutes and finally ceases 

 altogether. In six hearts observed under these conditions the average 

 time required for a complete loss of rhythmic beating was 76 minutes. 

 Artificial stimulation, pinching or turning the heart about in the 

 trough did not induce any regular beating. Rhythmical beating 

 was resumed, however, as soon as sea water was allowed to flow about 

 the heart for a few moments ; the rate of beat was in some instances 

 somewhat slow at first but soon became about the same as before 

 exposure to the sugar solution. Two of the above hearts which had 

 been exposed to sugar solution for a little over 2 hours recovered in 

 sea water within 3 minutes; one heart exposed to sugar solution for 

 3^ hours; recovered in a little less that 4 minutes. The three re- 

 maining hearts were returned to sea water within a few minutes after 

 the rhythmic beating had stopped and recovered in between 2f and 

 3 minutes. Duplicate records of the speed of the contraction-wave 

 were not secured in these experiments because of the variability of the 

 beating in sugar. In solutions in which three-quarters of the sea 

 water is replaced by sugar solution, i.e., 25 per cent sea water or 

 less, there is a constant decrement in the rhythmic beating and a 

 final loss of irritability; the time required for this loss is greater than 

 in pure sugar solution, varying from 2 to 3| hours. Attempts to get 

 duplicate records of the propagation-velocity in these solutions were 

 not successful. Some observations were made in 30 per cent sea water, 

 but the velocity of the contraction-wave over two or three segments 

 proved exceedingly slow and the observations showed poor agreement. 



