526 Andrews . — The Effect of Gases on Nuclear Division. 
periments the motionless aerobic Bacteria showed the total absence of 
oxygen. 
When oxygen was admitted, after each of these experiments, a cell- 
wall was produced in fifteen minutes. These and many other experiments 
performed in this way show that it is impossible for the nucleus to divide 
independently of the protoplasm. That the nucleus could not begin division 
in pure hydrogen, whereas in the control experiments it could, shows this 
to be true. That nuclear division advanced in pure hydrogen without the 
formation of the cell-wall is to be explained simply and only on the ground 
that the hydrogen could not penetrate quickly enough to prevent a certain 
advance in nuclear division or interfere with the vital processes of the 
nucleus, as it had with those of the more exposed cytoplasm. 
II. The Effect of Carbon Dioxide. 
In the second set of experiments, where carbon dioxide was used, the 
apparatus shown in Fig. 16 was not employed. This gas was purified and freed 
from all traces of oxygen and then washed with water and subsequently 
tested to see that no oxygen remained. Its interference both with proto- 
plasmic streaming and nuclear division was more marked than that of 
hydrogen. 
1. Effects of Carbon Dioxide on the Movements of Protoplasm. 
In the cells of the hairs of Momordica Elatcrmm the streaming of the 
protoplasm ceased in six minutes after admitting carbon dioxide. The 
specimens were left in a constantly flowing stream of carbon dioxide for 
three hours, during which time no movement of the protoplasm was 
evident. When oxygen was allowed to enter, the movement began again 
in ten minutes. In Trade scantia virginica the same effect and time-rela- 
tion was observed. 
2. Effects of Carbon Dioxide on Nuclear Division. 
Nuclei of Trade scantia virginica in the resting stage were left in 
pure carbon dioxide for two and one-half hours, and did not commence 
division. They seemed at the expiration of this time to be slightly dis- 
organized. Recovery of the nucleus was possible if the disorganization had 
not proceeded too far. Whenever nuclear division did occur after this 
disorganization it was always by karyokinesis. 
A cell of Trade scantia virginica , whose nucleus was near the close of 
the prophase stage, was left in carbon dioxide for three hours, but no 
further division of the nucleus occurred. After thirty minutes, oxygen was 
again admitted, when the protoplasm first began to move, then the nucleus 
to divide, completing its division and forming a cell-wall in one hour and 
forty minutes. This, as in the similar case of hydrogen, was somewhat 
