POISONS. 215 
affected by the nitrite, so it is the last thing to 
return during recovery. 
3. Caffein.—The effects of caffein on Sarsia may 
be best studied by immersing the animals in a 
saturated sea-water solution of the substance. In 
such solutions the Medusze float to the surface, in 
consequence of their lower specific gravity. I 
therefore used shallow vessels, in order that the 
margins of the nectocalyces might rest in the level 
of the water that was thoroughly saturated. The 
immediate effect of suddenly immersing Sarsia in 
such a solution is very greatly to increase the rate 
of the pulsations, and, at the same time, to diminish 
their potency. The appearance presented by the 
swimming motions is therefore that of a fluttering 
nature ; and such motions are not nearly so effectual 
for progression as are the normal pulsations in 
unpoisoned water. This stage, however, only lasts 
for a few seconds, after which the spontaneous 
motions begin gradually to fade away. Soon they 
altogether cease, though occasionally one among 
a number of Sarsize confined in the same saturated 
solution will continue, even for several minutes 
after the first immersion, to give one or two very > 
feeble contractions at long intervals. Eventually, 
however, all spontaneity ceases on the part of all 
the specimens, and now the latter will continue for 
a very long time to be sensitive to stimulation. At 
first several feeble locomotor contractions will be 
given in response to each stimulus; and as on the 
one hand these contractions never originate spon- 
taneously, while, on the other hand, paralyzed 
