5S2 MERKEL HENRY JACOBS 
(72) claims that not only Euplotes but also Stylonychia and Chil- 
odon and higher animals as well were completely killed by carbon 
dioxide in three minutes. Such low figures give grounds for the. 
suspicion that his gas was not pure or that some other disturbing 
factor was present. 
8. Vorticella nebulifera. This in many respects is the most 
interesting form studied. It presents a case where both vibratile 
structures (membranelles) and contractile ones (myonemes of 
the ‘bell’ and contractile filament of the stalk) are highly devel- 
oped, and it is a point of considerable interest to compare the 
effect of carbon dioxide on these two classes of structures in the 
same cell. Its effects are as follows. Almost instantly when the 
gas is turned on the animal is strongly stimulated and makes 
perhaps half-a-dozen violent contractions of the stalk, which 
then slowly relaxes, and thereafter so long as the gas is allowed to 
flow neither contracts spontaneously nor can be made to do so by 
mechanical stimuli. The time required to produce this paralysis 
of the stalk varies from thirty to sixty seconds. ‘The myonemes 
of the ‘bell’ are similarly affected and the animal remains 
fully expanded throughout the experiment. If the gas is not 
allowed to act too long, full and speedy recovery may occur on 
removal to the air. For instance, in one experiment after a five 
minutes’ exposure to carbon dioxide and a subsequent five min- 
utes’ exposure to the air the animals were all, normal in every 
respect. If the exposure to the gas is longer continued, however, 
permanent injury to the stalk results. After fifteen minutes the 
animals show a strong tendency to drop off of their stalks and the 
latter can be seen to be altered in appearance, the contractile 
filament becoming broken up into irregular refractive fragments 
and droplets. If the detached animals recover, they regenerate 
a new stalk. 
The effect on the membranelles is almost the reverse of that on 
the contractile structures. At first they may show a temporary 
cessation of movement but usually inside a few moments they 
begin beating again and may continue to do so forthree-quarters 
of an hour or more. Sometimes they stop temporarily and then 
start again even in the carbon dioxide while, removed to the air, 
