EFFECTS OF CARBON DIOXIDE ON PROTOPLASM. 21 



This characteristic of Colpidium is of some importance in con- 

 nection with the question already raised as to whether the differ- 

 ences in the ease of separation of the food vacuoles after exposure 

 to CO 2 are due to changes in the viscosity or in the specific gravity 

 of the protoplasm. In the case of the fine particles and the food 

 vacuoles of Colpidium we are evidently dealing with two materials 

 of different densities one heavier and the other lighter than the 

 protoplasm. If a change in the specific gravity of the latter 

 through the taking up or giving off of water were alone concerned 

 in facilitating separation, it is evident that a change that wonM 

 favor the movement of the food vacuoles would hinder that of the 

 fine particles and vice-versa. As a matter of fact, the movement 

 of both is favored at the same time. The logical conclusion, there- 

 fore, is that a decrease in viscosity rather than a change in specific 

 gravity is concerned, though it is by no means unlikely that changes 

 in specific gravity whose effects are, however, relatively insignifi- 

 cant may also occur. 



In concluding the section on Colpidium it may be worth while to 

 present in tabular form the behavior of this animal and of Para- 

 mcecimn in a typical experiment where both organisms were ob- 

 tained from the same culture and were subjected together to the 

 effects of CO,. 



EXPERIMENTS ON ARBACIA EGGS. 



Certain experiments, as yet unpublished, which the author has 

 made with a different end in view on the eggs of the sea-urchin, 

 Arbacia, confirm to a certain extent the conclusions arrived at in 

 the preceding sections. The experiments were primarily intended 

 to throw light on the relative efficiency of buffered solutions of the 

 same pH, but containing different amounts of CO., in producing 

 internal changes in cells. For the purpose of detecting such 

 changes, advantage was taken of the readiness with which centrif- 

 ugal force brings about a stratification of the materials found in 

 Arbacia eggs into four layers. This appearance was first de- 

 scribed by Lyon ('07) and has since been used with good effect 

 by Heilbrunn in following the changes in the viscosity of the proto- 

 plasm of these eggs at different stages of division, under the effects 

 of anjesthetics, etc. 



