RHYTHMIC PULSATION 343 



washed (inside and out) with a stream of fresh water''' before 

 being put in the non-electrolyte solution. No evidence was had 

 of an increase in muscular tone in sugar solutions, though pulsa- 

 tion usuallj^ ceased with the sphincter in the contracted condi- 

 tion. I had previously found (Crozier '15) that glycerin and 

 maltose would stimulate the skin of Holothuria surinamensis in 

 a sensory way; this effect probably had nothing to do with the 

 action of sugar solutions upon pulsation, since the glycerin and 

 maltose solutions did not behave differently from those of sucrose, 

 etc., which had been found not to stimulate. Pulsations, where 

 they did occur, were always of lower frequency in sugar solu- 

 tions than in the controls in sea water. 



VIII. ION EFFECTS 



^ a) Single salts. The relation of the salts of sea water to cloacal 

 pulsation and general irritability was studied by observing the 

 action of single electrolytes at equivalent concentrations (i.e., 

 isotonic with sea water), and the effects of various combinations 

 of these substances in the proportions at which they occur in 

 sea water. The method of procedure consisted in placing in the 

 desired salt solution freshly amputated cloacal ends of which 

 the pulsation rate had been determined previous to removal from 

 the animal. Before immersion the pieces were rapidly washed 

 by a stream of rain water from a wash bottle. Check experi- 

 ments showed that washing the outside and inside of the cloacal 

 end in this way did not have any effect upon the rate or duration 

 of subsequent pulsation of pieces reimmersed in sea water. Since 

 the excised pieces were immersed while in the condition shown 

 in A, figure 12, that is, before the inturning of the cut edges 

 had closed the cavity containing the radiating muscle strands, 

 the solution had abundant opportunity to gain access to the ele- 

 ments concerned in pulsation. Care was taken that the cavity 

 became filled with the solution surrounding the immersed piece 

 and that no air remained in it. Since the pumping movements 

 maintained a current of fluid through the cloaca, the solution 



^^ Check experiments showed that the washing had no effect on pulsation, 

 at least on its duration. 



