POISONS. 215 



affected by the nitrite, so it is the last thing to 

 return during recovery. 



3. Caff tin. — The eilects 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 Medusi^ 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 

 swimmino- motions is therefore that of a flutterinof 

 nature ; and such motions are not nearly so effectual 

 for progression as are the normal pulsations in 

 unpois;<ned 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 Sarsioe 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 severed 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 



