336 



W. J. CROZIER 



This effect was uniformly obtained in other experiments of 

 similar nature. 



b) Carbon dioxide. Carbon dioxide was a powerful agent in 

 suppressing pulsations. Tests were made by adding to sea 

 water small volumes of rain water charged with CO2. The car- 

 bonated water was slightly acid aside from its H2CO3. 



Experiment 79.2. July 11. Three freshly amputated eloacal ends 

 were immersed each in 200 cc. of sea water to which 2 cc. of 'carbonated 

 water' had been added. They did not pulsate in this mixture. After 

 ten minutes immersion the pieces were transferred to normal sea water. 

 Pulsations revived in 5 to 7 minutes. 



Concordant results were obtained by adding C02-water to solu- 

 tions containing pulsating pieces, the pulsations being rapidly 

 reduced in amplitude and usually stopped within a few minutes 

 when from 1 to 2 per cent of the 'carbonated water' had been 

 added. 



c) Urea. Urea likewise had a depressing effect upon pulsa- 

 tion. Fosse ('13) identified urea in echinoderms and their excre- 

 tory products. 



Experiment 38.2. June 24. Stichopus moebii, 27 cms. long; 68 sec- 

 onds for 10 pulsations at 25.1°; cloaca! end amputated and placed in 

 300 cc. sea water + 5 cc. fjr urea. 



This particular experiment is plotted at C in figure 27; it was 

 checked by four other experiments, which yielded the same result. 

 d) Light. With Holothuria surinamensis and H. captiva it 

 was previously found (Crozier, '14, '15) that light exerted a 

 distinctly toxic influence on the animals. It was therefore ex- 

 pected that sunlight would affect in some way the pulsation rate 



