EFFECTS OF CARBON DIOXIDE 531 
first it exhibits a shght negative response which, however does 
not last very long and is not so decided as in the case of many of 
the other forms. Very soon its movements, never very active, 
become markedly slowed, and for long periods there is either no 
locomotion at all or this is very slow.’ The membranelles and cilia, 
however, keep on beating up to the time of death, which in the 
majority of cases occurs in from three to six hours. These two 
structures in Blepharisma seem to have about the same resistance. 
Two phenomena which are particularly characteristic of this 
species are the marked change in form which occurs and the tend- 
ency towards the formation of large vacuoles in the protoplasm. 
The body, originally lanceolate, within an hour or two often 
becomes very broadly ovate or sometimes almost circular in out- 
line. Corresponding to the general variability of the species in 
other respects, there is a great individual variation in this regard 
also. Towards the end, considerable distortion of the body occurs 
but bursting is rare. 
7. Euplotes patella. This form, on account of its peculiar 
cuirass-like modification of the pellicle might be expected to show 
a high resistance, but such is not the case. Its resistance in 
general is somewhat below that of Paramecium aurelia. The 
effect of the carbon dioxide on it becomes apparent very early. 
It is not markedly stimulated, though it does show a negative 
response at first. The normal movements of locomotion dis- 
appear as a rule after five to ten minutes, although the membra- 
nelles sometimes keep on moving an hour longer. However, in 
most cases the average time of death is considerably less’ than 
this—generally under half-an-hour. The cell very early becomes 
much distorted and the pellicle of the ventral surface ruptures, 
allowing the escape of drops of clear protoplasm, while the macro- 
nucleus at the same time becomes very distinct and granular. 
Even after these changes have occurred, however, the membra- 
nelles continue their beat for a considerable time; the cirri are 
almost as resistant, though their movements are very irregular 
and uncoordinated towards the last. -The average time required 
for all movements to cease. varied in different experiments from 
about twenty-five minutes to a little over an hour. Rossbach 
