EFFECTS OF CARBON DIOXIDE ON PROTOPLASM. 19 



that might justly be raised in connection with the facts that have 

 been mentioned. The first is whether the behavior of Paramcecium 

 may not be due to the removal of oxygen by the current of CO 2 

 rather than to the action of the latter substance itself ; the second 

 is whether the changes in the readiness of separation of the food 

 vacuoles from the protoplasm may not be due to changes in the 

 specific gravity of the latter brought about by the absorption or 

 the giving off of water rather than to mere changes in viscosity. 

 As to the first question, it may be said that a vigorous current 

 of hydrogen, which must remove the oxygen at least as effectively 

 as the slower current of CO 2 , was not found to bring about the 

 sequence of changes described, even when allowed to flow for a 

 considerably longer time. It did, to be sure, appear after a time 

 to favor liquefaction of the protoplasm, but not only was its action 

 in this respect far slower than that of carbon dioxide, but in no 

 case were evidences of subsequent solidification observed though 

 the experiments were continued much beyond the time required for 

 the solidifying action of CO,. As to the second of the two ques- 

 tions, it may be noted that there appears to be no evident correla- 

 tion (as there should be if the chief factor were a change in the 

 specific gravity of the protoplasm) between the degree of swelling 

 in Paramcecium, which is evidently due to the taking up of water, 

 and the ease with which the food vacuoles may be separated from 

 the protoplasm. A second and even more convincing argument in 

 favor of the view here adopted will be given when the experiments 

 on Colpidium are described. 



EXPERIMENTS ON COLPIDIUM. 



The behavior of Colpidium when exposed to carbon dioxide 

 agrees in its essential features with that already described for 

 Paramcecium. There is a preliminary period of liquefaction fol- 

 lowed by increasing reversible solidification, and finally an irre- 

 versible coagulation. Colpidium is, however, more resistant to 

 CO 2 than Paramoscium and the time required- to bring about the 

 final coagulation is considerably greater. This difference is espe- 

 cially striking when the animals have first been placed in distilled 

 water in fact, it is so great in that case that it may be put to 



