28 M. H. JACOBS. 



culty in bringing about separation of the food vacuoles in the con- 

 trols, the increasing viscosity can not be followed as far as in 

 Paramoscium. In Arbacia eggs it is easy to produce solidification, 

 which in the cases here described was in every case reversible, at 

 least in the physical sense. On account of the complicating effects 

 of artificial parthenogenesis the physiological reversibility is more 

 difficult to demonstrate, but in a number of instances it was shown 

 in an entirely satisfactory manner. In one lot of Spirogyra solidi- 

 fication was obtained, but could not be produced in several other 

 lots subsequently studied, and until favorable material is again 

 available it will be impossible to make any definite statements 

 about the reversibility of the process. Finally, in Amoeba, all of 

 the appearances, at least, of solidification can be produced, though 

 in this animal it is impossible to test the matter by the method of 

 centrifugalization. 



Considering in its entirety the evidence which has been given, 

 there seems to be no doubt that carbon dioxide is an efficient agent 

 for changing the consistency of protoplasm reversibly in either 

 direction, the exact effects produced depending on the concentration 

 of the gas, the material experimented upon, the time of exposure 

 and the presence or absence of other dissolved substances in the 

 medium. Since CCX has these properties, and since it is so uni- 

 versally present in cells and is produced at different rates at dif- 

 ferent times, it seems not unlikely that it may prove to be an im- 

 portant factor in bringing about certain of the changes in viscosity 

 that accompany various physiological activities of cells. In the 

 case of dividing eggs the temptation is strong to attempt to corre- 

 late the striking .variations in the rate of CO 2 production observed 

 by Lyon ('04) with the equally striking changes in protoplasmic 

 viscosity described by Heilbrunn ('20), Chambers ('17) and oth- 

 ers. The chief difficulty in this case would appear to be that since 

 carbon dioxide can have either a liquefying or a solidifying effect, 

 the exact nature of the changes produced by it would be difficult 

 to predict in advance. 



In the case of amoeboid movement also the hypothesis that carbon 

 dioxide may be at least an important agent is an attractive one. 

 As a matter of fact, L. Loeb ('20) and Hyman ('17) have both 

 expressed the idea that some substance is produced as the result of 



