EFFECTS OF CARBON DIOXIDE ES) 
long time ceased. In the case of individuals exposed for two 
hours, however, no recoveries occurred although the drop was kept 
under observation for. twenty-four hours. The time required 
for recovery to occur depends on the length of time the gas has 
acted. After an exposure of five minutes, metabolic movements 
of the body begin in less than a half minute after contact with the 
air, and the animals may be entirely normal in ten minutes. After 
a longer exposure the time required is much greater. In’ one 
experiment after an exposure of thirty-four minutes, but few of 
the animals were in a state of normal activity after an hour-and- 
-a-half in the air, though at the end of four hours most of them 
showed no signs of injury and were normal in every respect. 
Peranema therefore represents a form in which the effects of 
earbon dioxide on locomotion and the contractile movements of 
the body are almost instantaneous, but which is killed only after 
a prolonged exposure. The point of greatest interest is that 
while certain movements of the body are brought to a standstill 
in a few seconds the flagellum may continue to beat for half-an- 
hour ormore. Weare therefore dealing with structures concerned 
in producing movements in the same cell which show a consider- 
able physiological difference. 
2. Euglena viridis(?). This form is in some respects more 
resistant and in others less resistant than Peranema. The time 
required for locomotion to cease is longer and the powers of 
recovery after an extended exposure greater, but the flagellum 
is much more sensitive and the length of time required to bring 
to an end all visible movements is considerably less. Like Pera- 
nema, Euglena shows no decided negative reaction to the gas as 
do many of the forms studied, though locomotion may persist for 
a few moments. Often the first effect of the gas is to cause a 
short temporary cessation of all movements, which quickly reap- 
pear. Soon, however, movements of progression cease andthe 
organisms show signs of life only by vibrating movements which 
are due to the abnormal beat of the flagellum. These gradually 
_ cease and the animals sink to the bottom of the drop motionless 
and perfectly extended. The time required to produce cessation 
of all movement varies from two or three to ten minutes. The 
