THE EFFECT OF CYANIDES ON PROTOPLASM. 315 



exposure of 66 minutes to HCN solution, ten one minute readings 

 again taken. Temperature of room 21.7 C. 



The 10, 25 and 66 minute readings were repeated using solu- 

 tions of HCN up to 7V/2,ooo. Similar readings were also taken 

 using sea-water instead of HCN solutions. These served as con- 

 trols. Each time that a new sea-urchin was used, the diameters 

 of the eggs were first measured to be sure that they were approxi- 

 mately the same size as eggs which had been previously used. 



As previously stated, the HCN was drawn over into distilled 

 water and then diluted with sea-water. The original HCN solu- 

 tion (with distilled water) usually reached its saturation point as 

 an N/i^o HCN solution. In order to bring this to an N/$oo 

 HCN, an amount of sea-water almost equal to the original 

 amount of distilled water had to be added. This in itself, there- 

 fore, was a 57 per cent, solution of sea-water and the change in 

 volume of the eggs might very well be due to that hypotonicity 

 instead of to the effect of the HCN. This was checked by adding 

 to the control solutions of sea-water, as much distilled water as 

 was contained in the various concentrations of HCN. That is, 

 the control for the N/^oo HCN was a 57 per cent, sea-water 

 solution ; for the N/$oo HCN a 74 per cent, sea- water and for the 

 N/2,ooo HCN a 93 per cent, sea-water solution. The results 

 with these various controls showed that only in the high dilutions, 

 i.e., 57 per cent., 67 per cent, and 74 percent, sea-water solutions, 

 did this hypotonicity have any appreciable effect on the volume of 

 the eggs, but even this increase was much less than the increase in 

 volume of the eggs previously exposed to the HCN solution. 

 The dotted curve in Fig. i marked Control A is the control in 

 100 per cent, sea water, while the curve marked Control B is the 

 control in 67 per cent sea-water (comparable to the N/4.OO HCN). 

 The controls for the other concentrations have been omitted to 

 avoid confusion, but in every case the volumes of the eggs in the 

 controls were less than the volumes in the respective HCN solu- 

 tions. In other words, the volumes of the eggs in the HCN solu- 

 tions as shown in Fig. I are slightly greater than they would be if 

 the HCN solutions had been entirely made up with sea-water. 

 Since the KCN solutions were made up with sea-water only, 

 these precautions were unnecessary for that series of experiments. 



