EFFECTS OF CARBON DIOXIDE ON PROTOPLASM. 23 



sea water to which CO 2 has been added with those of a similar 

 solution in which the same pH has been produced by adding an- 

 other acid e.g., HC1, cautiously, drop by drop, and shaking 

 vigorously after each addition to remove the CO. 2 set free from 

 the bicarbonates by the acid. 



The results of one experiment of this sort may be given here.. 

 The exposures to carbon dioxide and to centrifugal force were 

 those already mentioned. The numerical values of the pH of the 

 solutions are only approximate, since the " salt errors " of the in- 

 dicators used for determining them were disregarded, but as the 

 error was in each case the same for the two solutions which were 

 being compared, the general results obtained were not thereby 

 affected. 



TABLE II. 



EFFECTS OF CENTRIFUGAL FORCE ON Arbacia EGGS EXPOSED FOR 5 MINUTES 

 TO SEA WATER OF DIFFERENT pH VALUES. 



pH (approximate) pH regulated by adding CO.... pH regulated by adding 



HC1 and then removing 

 CO,. 



S.o Stratification complete. Stratification complete. 



?.o Stratification complete. Stratification complete. 



6.0 Stratification decidedly incom- Stratification complete. 



plete. 

 5-5 No stratification. Stratification complete. 



It appears from this experiment that the effects of carbon 

 dioxide are primarily internal and depend on the absolute concen- 

 tration of this substance rather than on the pH of the solution. 

 These results are in agreement with those obtained by the author 

 with other material and described in previous papers ('20-0. 5 2O-fr). 



The solidifying effect of .CO* is at least to a certain extent re- 

 versible. In several experiments eggs exposed to saturated sea 

 water for 5 minutes were divided into two lots. The first lot was 

 tested immediately and found to be solidified, giving no evidence 

 of stratification after centrifugalization. The second lot was al- 

 lowed to stand exposed to the air in a shallow dish for 30 minutes 

 to permit the C(X to escape, or in some cases fresh sea water was 

 also added. In either event centrifugal force produced normal 

 stratification, showing that the eggs had again returned to the liquid 



