42 DYNAMICS OF NERVE CELLS. I 



The ganglion of the heart of Limulus polyphemus occupies a median 

 dorsal position on that organ; the nerve cells occupy a position over 

 the posterior five or six segments of the heart and are connected with 

 the anterior muscular segments by a median and two lateral nerves. 

 This ganglion, which may be 10 or 15 cm. in length, can be dissected 

 from the underl}dng tissue with ease and maintain functional connec- 

 tion with the muscle of the anterior segments. 



In the experiments to be described a method was finally adopted in 

 which a Dewar flask contained an immersion fluid, either sea water or 

 Limulus blood serum. A system of glass tubes provided for renewal 

 of the fluid at different temperatures which were recorded by a stand- 

 ard thermometer graduated to 0.1 °C. Either the posterior segments 

 of the whole heart, or the dissected ganglion, depended into the fluid 

 through an opening in a paraffined cap. The two anterior segments 

 were pinned to the cap, enclosed in a moist chamber, and kept at a 

 constant temperature. The contractions of the anterior segments 

 were graphically recorded and served as an index not only of the rate 

 but of the effective strength of the impulses reaching the muscles. 

 The study in its ramifications has extended to about 200 Limulus 

 hearts. 



Observations on the Whole Heart. 



At Beaufort, N. C, the laboratory sea water was 27.7°C. and 

 the average rate of 60 hearts was 23 beats per minute, while, at 

 Woods Hole, the laboratory sea water was 20.1°C. and the average 

 rate of 48 hearts was 11.6 per minute. A temperature coefficient of 

 about 2.6 (^lo) is obtained from these figures, calculating for the 10° 

 interval. The individual hearts show wide variations in rate, and 

 since the sea water of the two locahties differs somewhat in concen- 

 tration, this average coefficient for the whole heart can be considered 

 only an approximation. 



To illustrate the magnitude of the temperature coefficient of the 

 whole heart for what may be considered a fairly nonnal range of tem- 

 perature, ten experiments have been selected from our series — experi- 

 ments in which it so happened that observations were made at exactly 

 15 and 25 °C. The results are given in Table I. The experiments 

 given in Table I show that the whole heart of Limulus, subjected to 



