606 WOLFGANG F. EWALD 



few minutes by means of a filter pump (at about 300 mm. of 

 mercury pressure) they become positive immediately and remain 

 so as long as they are left in the water. Transferred into fresh 

 water they become negative again with equal velocity. This 

 is one of the strongest and most striking reactions. Traces of 

 metal acted in the reverse sense. If traces of copper (Cu2 con- 

 centration = 2.10"'^) are added to the seawater, all positive 

 animals soon become negative and remain so. This effect is in 

 accordance with the experiments on oxydation in the sea-urchin 

 egg, where traces of metal also acted in the same sense as alkali 

 and increase in temperature. I did not, however, repeat this 

 experiment more than three or four times with different animals. 



I found no marked positivating or negativating effect with 

 narcotics, of which alcohol, ether and chloroform were tried, 

 though the tendency was rather in the former direction. They 

 would, however, disorient the animals, like calcium, causing 

 them not to assemble at the poles of the vessel but to swim about 

 freely in all directions. 



Experiments with potassium cyanide, strychnine, oxygen and 

 hydrogen peroxyde met with no success. Finally, I made ex- 

 periments with changes in concentration. The result was the 

 same observed by Loeb with Copepods: increase in concentra- 

 tion had a positivating effect, decrease a negativating one. My 

 best hypertonic solution contained 1 gram of pure crystalline 

 NaCl in 100 cc. of seawater. The effect was very strong. To 

 exclude the possibility, that the higher concentration of Na 

 ions was responsible for this result, I made a hypertonic solu- 

 tion of magnesium chloride which could in no way be suspected 

 of a specific positivating salt action. The positivating effect 

 was less marked but sufficiently evident. I am therefore justi- 

 fied in concluding, that hypertonicity alone has a positivating 

 influence, though in the first case it may have been seconded 

 by the effect of the increase in Nations. Increase in concen- 

 tration has the opposite effect. Seawater mixed with fresh 

 water in the proportion of 7:1 quickly makes positive animals 

 negative and prevents negative ones from becoming positive. 



