EFFECTS OF CARBON DIOXIDE OX PROTOPLASM. 27 



respectively. The four lots, together with a control, were then 

 centrifuged as before, with the following results: In the control 

 some cells showed a separation of the chloroplasts, while others 

 did not ; in those exposed for 2 minutes practically all showed com- 

 plete separation ; in those exposed for 4 and for 8 minutes there 

 was somewhat less separation (the amount being approximately 

 the same as in the control), while with the i6-minute exposure 

 there was very little separation and the filaments showed a certain 

 apparent brittleness, being to some extent broken into pieces during 

 their transfer to a watch glass for examination. 



As to the reversibility of these effects on Spirogyra, it may be 

 said that observations on this point are much more difficult to 

 make than in the case of the motile Protozoa, and in the instances 

 mentioned satisfactory determinations were not made. It has 

 since been found with the more abundant material recently avail- 

 able that the filaments in which the exposure has been sufficient to 

 produce decided liquefaction are not at all injured by the process, 

 continuing to grow after the treatment in a normal manner. But 

 whether or not recovery is possible after solidification can be deter- 

 mined only when Spirogyra which shows this behavior as clearly 

 as did the first lot studied is again available in considerable quan- 

 tities. 



DISCUSSION OF RESULTS. 



It appears from the results obtained on four animal cells and on 

 one plant cell that carbon dioxide can bring about changes in proto- 

 plasmic viscosity of two sorts. Clear evidence of liquefaction is 

 obtained in Paramccciurn, Colpidiuni and Spirogyra. Observa- 

 tions on this point are not available for Arbacia eggs, and in the 

 case of Ainccba, while the results are apparently in agreement with 

 those already mentioned, they are based on mere appearances, and 

 are therefore perhaps not so certain as the others. In every case 

 where liquefaction was shown to occur this change could be shown 

 to be reversible. 



As to solidification, the clearest case is furnished by Para- 

 rnoeciuin, where the process and its complete reversibility up to a 

 certain point can easily be demonstrated. Conditions in Colpidiwn 

 are almost as favorable, except that on account of the greater diffi- 



