NATURAL RHYTHM. 173 
exposed to such influence. Jastly, it will be ob- 
served from the above table that the unnatural 
amount of activity displayed by the organism while 
in the oxygenated water entailed on it a consider- 
able degree of exhaustion, as shown by the fact 
that even a quarter of an hour after its restoration 
to normal water its original degree of energy had 
not quite returned. 
Carbonic acid—As might be expected, this gas 
has the opposite effects to those of oxygen. It is 
therefore needless to say more about this agent, 
except that if administered in large doses it destroys 
both spontaneity and irritability. Nevertheless, if 
its action is not allowed to last too long, the Medusze 
will fuliy recover on being again restored to normal 
sea-water. 
Nitrous oxide—This gas at first accelerates the 
motions of Sarsia, but eventually retards them. 
I omitted, however, to push the experiment to the 
stage of complete anesthesia, which would doubt- 
less have supervened had the pressure of the gas 
been sufficiently great. 
Deficient aération—It may now be stated that 
the Medusve are exceedingly sensitive to such slight 
carbonization of the water in which they are con- 
tained as results from their being confined in a 
limited body of it for a few hours. The rhythm 
becomes slowed and the contractions feeble, while 
the pauses between the swimming bouts become 
more frequent and prolonged. If the water is not 
changed, all these symptoms become more marked, 
and, in addition, the rhythm becomes very irregular. 
