SAMUEL ERNEST POND 815 



The majority of the records have been taken from two points situated 

 a short distance apart in the middle region. The results are not 

 combined in a single set of figures because the same conditions do 

 not appear to prevail in all regions. Each experiment by itself how- 

 ever, indicates that a lowered electrical conductivity of the medium 

 is always associated with a reduction in the propagation- velocity 

 of the contraction-wave over the region under observation. It will 

 be noted that in all of the experiments the ratios of velocity with 

 respect to conductivity are of the same order. 



Another variable feature has been encountered in the irregular 

 behavior of the hearts of animals which were kept in captivity for 

 more than two months at Woods Hole. After being exposed in the 

 trough for a few hours such hearts would often reverse their direc- 

 tion of beat, or would become arhythmical. In the case of animals 

 fresh from the shore and others which had been artificially fed with 

 small fish the hearts showed regular behavior and have provided 

 consistent records, from which Table II has been compiled. 



In running sea water the propagation-velocity of a healthy heart 

 may be regularly so high as 80 cm. per second, but this velocity is 

 not always found if the same regions are com^pared. In the eight 

 experiments reported the velocity varies from 63 to 81 cm. per second. 

 The average velocity is in the neighborhood of 70 cm. per second. 

 The concentrations given in the second column of Table II are ex- 

 pressed as the fractional part of sea water present in the mixed so- 

 lutions, i.e., a mixture of 8 parts sea water and 2 parts isotonic sugar 

 solution is designated as "0.8 Sw.'^ The conductivity of the sea 

 water is taken as unity, and the proportional conductivity of the mix- 

 tures if calculated from the experimental determinations of resist- 

 ance. The velocity of the propagated disturbance is expressed in 

 centimeters per second. These two sets of determinations are com- 

 bined in the last column as the ratio of velocity v with respect to 

 conductivity c. All of the calculations are subject to an error in- 

 troduced in reading the records, varying from 5 per cent at the speed 

 of 80 cm. per second to 2 per cent at 20 cm. per second. 



A number of observations were made with reference to the aera- 

 tion of the solution. Limulus hearts examined in mixed solutions 

 made with sea water which had been shipped to Worcester from 



