538 MERKEL HENRY JACOBS 
irreparable injury probably occurs before the membyranelles cease 
beating) while in other cases, the animal is capable of full recovery 
long after all movements have ceased, e.g., flagellates and Vorti- 
cella. Some animals which are otherwise fairly resistant to car- 
bon dioxide, as shown by their powers of recovery after a pro- 
tracted exposure to it, or by the long continuation of visible 
movements, show its effects very quickly by their inability to 
carry on normal locomotion in its presence. Peranems is the 
most striking example of this condition, Euglena and Euplotes 
also being relatively quickly affected. In their primary response 
the different forms also show distinct differences. The three 
species of Paramecium studied as well as Colpidium, and Chilo- 
monas show a decided negative reaction and an effort to escape 
from it. This reaction is less marked in Blepharisma and Eu- 
plotes, while in the other forms it is practically lacking, probably 
because normal movements are so quickly interfered with. (En- 
tosiphon was not studied in this connection.) It will be seen, 
therefore, that the different forms studied show certain charac- 
teristic differences in reactions and general resistance to carbon 
dioxide. 
It has already been pointed out that there is a certain amount 
of individual and cultural variation in the same species, which 
makes it impossible to put in exact quantitative form the time 
in which death occurs, etc. Nevertheless the relative resistance 
of each form as compared with other forms from the same culture 
is fairly constant and furthermore it is at least possible to say that 
certain forms always have a high, and others always a low resist- 
ance. While some forms may ‘overlap,’ others, as for example 
Colpidium and Coleps, never do. 
The observations here recorded are not the first that have been 
made on the differences in resistance to carbon dioxide shown 
by different organisms. Frinkel (’88) studied the effect of this 
substance on various bacteria with the result that some were found 
to thrive almost as well as in air, others had their development 
checked but were not killed, while others were quickly destroyed. 
Lopriore (’95) also, in his careful experiments on the effects of 
carbon dioxide on the spores and mycelia of fungi and the pollen 
