EFFECTS OF CARBON DIOXIDE 541 
cases (Vorticella) the action of carbon dioxide on these two classes 
of structures is exactly opposite, the contractile elements being 
first stimulated and then paralyzed and the vibratile ones often 
temporarily stopped and then started again. 
4. Ordinary cilia and their modifications, membranelles and 
cirri when present in the same cell show approximately the same 
resistance. Flagella show great variation, that of Kuglena being 
paralyzed in a few minutes and those of Chilomonas and Ento- 
siphon remaining active for several hours. 
5. In ciliates in general, with the exception of the specialized 
Vorticella, recovery after complete cessation of movement is 
impossible; in the flagellates, movement cease long before the cell 
is permanently injured. 
6. The general effects of carbon dioxide on the cell are to cause 
(a) cessation of movement, (b) absorption of water and consequent 
swelling, (c) injury to the cell wall, (d) death and coagulation of 
the protoplasm. 
* 
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