522 MERKEL HENRY JACOBS 
ing absolutely final conclusions; it is thought, however, that fur- 
ther work will not materially alter the results arrived at in this 
paper. 
The general method employed in studying the effects of carbon 
dioxide on the forms in question was to subject them, in a drop of 
culture fluid, to a continuous stream of this gas in an Engelmann 
gas chamber. The drop of liquid containing them was placed 
on a slide or cover glass and the latter inverted in the usual way 
over the opening of the gas chamber, the joints being made air- 
tight with vaseline. The observations were made entirely with 
the compound microscope, chiefly with a Leitz 3-objective, 
although in doubtful cases the 7-objective was also employed. 
The points especially noted were the time required to stop normal 
locomotion, the time required completely to stop the beat of the 
cilia, flagella, ete., and the longest possible exposure after which 
recovery is possible when normal conditions are restored. In 
addition, incidental observations were made on the general behav- 
ior of the organisms and the visible structural changes produced 
in the cell by carbon dioxide. 
The gas used in the experiments was generated in the apparatus 
designed by McCoy, from marble and C. P. hydrochloric acid 
diluted in the proportion of one part of acid to four of water. 
Before coming in contact with the animals it was passed through 
two wash bottles filled with a solution of sodium carbonate to 
remove any traces of hydrochloric acid that might be present and 
also to ensure thorough saturation with water vapor. That no 
appreciable amount of hydrochloric acid was left in the gas was 
shown by conducting it into a silver nitrate solution, which in the 
course of two hours showed no traces of a precipitate or even of a 
cloudiness. The gas after being thus purified was conducted 
successively through four Engelmann chambers, each placed on 
the stage of a microscope, and connected by rubber tubing in such 
a way that the same gas passed through all of them. This arrange- 
ment was found very useful, not only in making comparisons 
between different species under as nearly identical conditions as 
possible, but also in facilitating a larger number of independent 
observations on individuals belonging to the same species. 
